THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


OQ     a 

I   ' 

s  "S 


IN 


ADVANCED  PHYSIOLOGY, 


BY  LOUIS  J.   RETTGER,  A.  M., 

Professor  of  Biology  in  The  Indiana  State  Normal  School. 


TERRE  HAUTE,  IND. 
THE  INLAND  PUBLISHING  COMPANY 

1898 


Copyrighted,  1898, 
BY  Louis  J.  RETTGER. 


-BECKTOLD  — 

PRINTING  AND  BOOK  MFG.CO. 
ST.  LOUIS,  MO. 


PREFACE. 


There  are  two  extremes  open  in  writing  a  brief  treatise 
on  any  natural  science.  One  is  to  state  briefly  and  explic- 
itly those  facts  which  are  seriously  questioned  by  no  one. 
It  is  to  enumerate  and  tabulate  what  is  definitely  known 
about  the  subject.  In  the  field  of  animal  physiology  there 
is  much  which  is  "settled"  information,  and  which  it  is  be- 
lieved, will  not  be  materially  changed  by  the  developments 
of  the  future.  Most  of  the  gross  anatomy  is  finished,  by  no 
means  all,  but  many  points  in  histology  are  determined, 
while  in  pure  physiology  there  are  fewer  things  that  are  con- 
sidered explained.  Thus  the  phenomena  of  respiration  and 
the  dynamics  of  the  blood  flow  are  to  a  very  large  extent 
known  in  terms  of  chemical  and  physical  laws.  To  limit  a 
book  to  this  would  be  to  make  it  stereotyped,  dead,  and  leave 
the  reader  with  the  impression  that  physiology  like  Sanskrit 
was  finished,  and  like  every  finished  problem  had  no  longer 
a  living  interest  of  its  own.  Most  of  the  ordinary  text- 
books err  on  this  side.  They  state  ex  cathedra,  fact  after 
fact,  they  seldom  give  the  reasons  which  have  led  physi- 
ologists to  adopt  the  views  in  question,  and  they  seldom 
leave  the  idea  that  many  things  are  still  being  studied  with 
the  hope  that  more  study  will  give  new  light.  Most  text- 
books leave  the  mind  of  the  student  with  the  belief  that  all 
has  been  told,  that  there  is  nothing  more  to  add,  and  that 
therefore  there  is  no  need  for  him  to  try  to  improve  on  the 
text-book,  by  making  his  own  observation.  The  feeling  of 
the  authority  of  the  text-book  in  physiology  has  robbed 
many  a  student  of  the  desire  to  investigate  the  subject 
further.  L,ike  the  Scholastics  of  the  Middle  Ages  they  turn 
to  the  book  as  to  Aristotle,  fully  convinced  that  all  know- 
ledge is  contained  in  it,  and  that  what  is  not  contained  is 
impossible  of  access. 

The  other  extreme  is  to  give  in  detail  all  the  scientific 
controversies  of  the  past  and  present.  It  is  to  state  indis- 
criminately pros  and  cons  until  the  conviction  settles  over 
one  that  nothing  is  definite  and  all  is  confusion.  Especially 
true  is  this  when  these  conflicting  views  are  at  once  pre- 
sented to  the  beginner  in  the  subject. 

(iii) 


IV  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

There  are  in  physiology,  as,  possibly,  in  all  other 
sciences,  many  problems  at  present  which  admit  of  different 
interpretations,  and  which  must  be  referred  to  the  investi- 
gations of  the  future  for  their  correctness  or  their  faultiness. 
It  would  not  be  treating  the  reader  right  to  shower  him 
with  all  sides  of  these  questions,  but  the  author  has  endeav- 
ored to  present  that  view  in  each  case  which  seems  most 
generally  accepted  by  scientific  men,  and  awaiting  future 
verifications  to  show  the  value  of  the  claim.  By  taking 
this  median  course  it  is  believed  that  the  book  will  give  to 
its  readers  all  of  the  main  known  facts,  and  in  addition 
acquaint  them  with  many  of  those  questions  which  are  now 
demanding  the  attention  of  physiologists.  This  will  put 
the  science  of  physiology  in  its  true  light,  it  will  show  that 
it  is  a  living  science,  still  at  work  trying  to  interpret  living 
problems.  While  it  will  show  the  present  limitations  of 
our  knowledge  it  will  suggest  future  possibilities. 

It  is  hoped  that  the  study  of  this  book  may  result  in  a 
more  lively  appreciation  of  physiological  phenomena,  and 
an  added  interest  in  teaching  the  subject  in  our  common 
schools. 

It  has  been  the  aim  to  choose  the  illustrations  for  this 
book  with  the  greatest  possible  care.  They  have  been 
selected  from  quite  a  number  of  sources,  and  the  proper 
credit  has  in  each  case  been  given  with  every  figure.  Quite 
a  number  of  the  histological  illustrations  are  from  Schafer's 
Essentials  of  Histology.  The  author  desires  hereby  to 
thank  Messrs.  L,ongmans,  Green  &  Company,  the  publish- 
ers of  that  prince  of  text-books,  Quain's  Anatomy,  for  their 
permission  to  reproduce  several  of  the  illustrations  found 
therein.  The  colored  plates  on  the  circulation  of  the  blood 
have  been  made  possible  by  their  courtesy.  The  author  is 
also  under  many  obligations  to  D.  Appleton  &  Company, 
publishers  of  Osier's  Practice  of  Medicine,  for  permission 
to  reproduce  the  colored  plates  illustrative  of  the  nervous 

Louis  J.  RETTGER. 
Terre  Haute,  Indiana, 
Aug.  12,  1898. 


SABLE  OF  (CONTENTS. 


PAGE. 

Introduction 1 

CHAPTER  I. 
An  Epitome  of  the  History  of  Physiology. 

Hippocrates.  Aristotle.  Praxagoras.  Herophilus  and  the  Alex- 
andrian School. "  Galen.  Vesalius.  Servetus.  Fabricius. 
Harvey.  Later  investigators 5 

CHAPTER  II. 
The  Cell  and  its  Life. 

Historical  view.  A  typical  cell.  The  division  of  the  cell.  Physi- 
cal basis  of  heredity  22 

CHAPTER  III. 
The  Teaching  of  Physiology  and  the  Public  Health. 

History  of  Sanitation.  Bacteriology.  Bacteria.  How  germs 
produce  disease.  Theories  of  immunity.  Unsolved  prob- 
lems. Practical  guidance.  Rules  of  Indiana  Board  of> 
Health 29 

CHAPTER   IV. 
General  Definitions. 

Anatomy.      Comparative    Anatomy.      Histology.      Embryology. 

Classification 46 

CHAPTER  V. 
The  Blood. 

General  points.  Amount.  Composition.  Red  corpuscles,  (size, 
form,  color,  surface,  composition,  consistency,  origin,  de- 
struction). Haemoglobin.  Spectrum  of  haemoglobin.  Blood 
crystals.  White  corpuscles.  Blood  plates.  Blood  plasma. 

Coagulation.     Serum.     Phenomena  of  osmosis 49 

(v) 


VI  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

CHAPTER  VI. 
The  Supporting  Tissues.  PAGE. 

The  Skeleton.  Minute  structure  of  bone.  Origin  and  growth  of 
bone.  Process  of  ossification.  Chemical  composition  of 
bone.  Cartilages.  Connective  tissues  proper.  Humors. 
Formation  of  cartilage  and  connective  tissues.  Hygiene  of 
supporting  tissues.  Joints.  Ligaments  75 

CHAPTER  VII. 
Muscles  and  the  Phenomena  of  Contraction. 

Kinds  of  Muscles.  Voluntary  muscles.  Minute  structure.  Growth 
of  muscle.  Finer  structure  of  the  muscle  fibre.  Plain  mus- 
cular tissue.  Cardiac  muscle.  Chemistry  of  muscle.  Elas- 
ticity. Muscle  stimuli.  A  single  contraction.  Tetanus. 
Wave  of  contraction.  Lifting  power  of  muscles.  Changes 
in  volume.  Muscle  fatigue-.  Blood  supply  of  muscles. 
Electrical  phenomena  in  muscles.  Wave  of  negative  varia- 
tion. Rigor  mortis.  Source  of  muscular  energy.  Mechan- 
ics of  muscles.  Levers.  Mathematics  of  levers.  Hygiene 
of  muscles 112 

CHAPTER  VIII. 
The  Circulation. 

General  arrangement.  Route  of  one  complete  circulation.  The 
heart  (position,  coverings,  cavities,  vessels  arising  from, 
valves  of  heart).  The  arterial  system.  The  venous  system. 
The  pulmonary  circulation.  The  portal  circulation.  His- 
tology of  arteries,  veins  and  capillaries.  Phenomena  of  the 
heart's  beat  (rate,  systole,  diastole,  filling  of  heart,  sounds 
of  heart).  Cardiograms.  Pathological  sounds  of  the  heart. 
Amount  of  blood  forced  out  per  beat.  Energy  and  work 
of  the  heart.  Innervation  of  the  heart.  The  dynamics  of 
the  blood  stream.  Arterial  pressure.  Venous  pressure. 
Pressure  in  capillaries.  Rate  of  blood  flow.  Time  of  one 
complete  circulation.  Pulse  (cause,  kinds  of,  rate,  meas- 
urements of).  Innervation  of  blood-vessels.  Changes  in 
the  circulation  at  birth 146 

CHAPTER   IX. 
The  Lungs  and  the  Processes  of  Respiration. 

Anatomy  of  respiratory  system.  Pathological  conditions  of  sys- 
tem. Mechanics  of  respiration.  Ventilation.  Chemistry  of 
respiration.  Phenomena  of  external  respiration.  Dalton's 
law  of  gases.  The  role  of  the  red  corpuscles.  Phenomena 
of  internal  respiration.  Elimination  of  carbon  dioxide.  The 
innervation  of  the  respiratory  system 202 


TABLE    OF    CONTENTS,  Vll 

CHAPTER  X.  PAGE. 

The  Larynx  and  the  Production  of  Articulate  Speech. 

Anatomy  of  larynx.     Manipulation  of  larynx  in  the  production  of 

sounds.     Range  of  human  voice.     Vowels.     Consonants —       239 

CHAPTER  XL 
Glands  and  the  General  Physiology  of  Secretion. 

Historical.  Secretion.  Anatomy  of  glands.  Process  of  secre- 
tion. Histological  changes  in  secreting  cells.  Innervation 
of  glands ..  249 

CHAPTER  XTI. 
The  Digestive  Organs  and  their  Anatomy. 

Mouth.  Teeth.  Structure  of  a  typical  tooth.  Hygiene  of  the 
teeth.  Development  and  origin  of  the  teeth.  Tongue. 
Papillae.  Taste-bulbs.  Gullet.  Stomach.  Gastric  glands. 
Small  intestine.  Villi.  Large  intestine.  Mucous  glands. 
Pancreas.  Liver.  Thyroid  gland.  Spleen.  Adrenal  bodies. 
Thymus  gland.  Carotid  gland.  Coccygeal  gland.  Pituitary 
body 264 

CHAPTER  XIII. 
Foods  and  their  Physiological  Value. 

Losses  of  the  body.  Classes  of  foods.  A  mixed  diet.  Relative 
amounts  in  an  average  daily  diet.  Flavors,  condiments, 
stimulants.  Alcohol.  Physiological  effects  of  alcohol  308 

CHAPTER  XIV. 
Digestion  and  the  Digestive  Agents. 

Historical.  Saliva  and  salivary  digestion.  Theory  of  hydrolysis. 
Stomach  and  gastric  digestion.  Pepsin.  Pancreatic  juice. 
Trypsin.  Amylopsin.  Steapsin.  Bile.  Bile  salts.  Bile 
pigments.  General  function  of  bile.  Intestinal  juice.  ...  327 

CHAPTER  XV. 
Absorption  and  the  Routes  of  Food. 

Absorption  of  peptones.  Absorption  of  the  sugars.  Absorption 
of  the  fats.  General  physiology  of  the  liver.  Glycogen. 
Hepatic  action  on  albumens.  Formation  of  urea 352 


Vlll  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

CHAPTER  XVI.  PAGE. 

Nutrition  and  the  Metabolic  Changes  in  the  Tissues. 

General  questions.  Uses  of  the  classes  of  foods.  Use  of  proteids. 
Disintegration  of  living1  tissue.  Formation  of  urea.  For- 
mation of  C02.  Reconstruction  of  living  tissue.  Use  of  fats 
and  sugars.  Nutritive  equilibrium.  Kreatin.  Kreatinin. 
Inter-relation  of  fats  and  carbohydrates 365 

CHAPTER  XVII. 
The  Maintenance  of  the  Animal  Heat. 

Normal  temperature  of  body.  Warm-blooded,  cold-blooded  ani- 
mals. Variations  in  temperature.  Conditions  affecting  the 
temperature.  The  regulation  of  the  temperature.  Thermo- 
genic  nerves.  Quantitative  determinations  of  the  source 
and  expenditure  of  heat.  The  amount  of  heat  lost  by  the 
body 376 

CHAPTER  XVIII. 

The  Kidneys,  the  Skin  and  the  General  Physiology  of 
Excretion. 

Kidneys.  Anatomy  of  urinary  organs.  Circulation  through  kid- 
neys. Uriniferous  tubules.  Urine.  Composition  of  urine. 
Source  of  the  urea.  Skin.  Epidermis.  Dermis.  Nails. 
Hairs.  Sebaceous  glands.  Sweat  glands.  Nerves  of  sweat 
glands.  Composition  of  sweat 385 

CHAPTER  XIX. 
The  Anatomy  and  Physiology  of  the  Nervous  System. 

Nerve  systems.  Nervous  elements.  Nerves.  Nerve  Trunks. 
Plexuses.  Nerve  centers.  Ganglia.  Dura  mater.  Pia  mater. 
Arachnoid  membrane.  Spinal  cord.  Spinal  nerves.  Brain. 
Weight  of  brain.  Convolutions.  Interior  of  brain.  Ven- 
tricles. Cranial  nerves.  Sympathetic  system.  Histology 
of  nervous  system.  Neurons.  Minute  structure  of  nerves 
and  nerve  trunks.  Gray  fibres.  Development  of  nerves. 
Regeneration  of  nerves.  Neuroglia.  Nerve  stimuli.  Nature 
of  a  nervous  impulse.  Kinds  of  nerve  fibres.  Finer  archi- 
tecture of  central  nervous  system.  Arrangement  of  motor 
neurons.  Arrangement  of  sensory  neurons.  Medulla. 
Function  of  cerebellum.  Function  of  midbrain.  Function 
of  cerebrum.  Localization  of  centers  in  the  brain.  Physi- 
ological topography  of  the  brain.  Consciousness.  Sleep. 
Hypnotic  phenomena.  Time  relations  in  psychic  phe- 
nomena. Personal  equation 409 


TABLE    OF   CONTENTS.  ix 

CHAPTER  XX. 
The  Organs  of  Special  Sense.  PAGE. 

Common  sensations.  Special  sensations.  Structure  of  an  organ 
of  special  sense.  Neurosis.  Psychosis.  Development  of 
the  special  senses.  The  objectification  of  our  sensations. 
The  relation  between  neurosis  and  psychosis.  The  psycho- 
physical  law.  Confusion  of  sensations  and  inferences  from 
sensations  469 

CHAPTER  XXL. 
Touch,  Temperature,  Muscular  Sense,  Taste,  Smell. 

The  anatomy  of  the  end  organs  of  touch.  Pacinian  corpuscles. 
Tactile  cells.  End  bulbs.  Touch  corpuscles.  The  absolute 
touch  sensitiveness.  The  power  of  localization  and  the  touch 
areas.  The  sense  of  temperature.  The  muscular  sense. 
The  sense  of  taste.  Taste  bulbs.  The  nature  of  a  taste 
sensation 477 

CHAPTER  XXII. 
The  Ear. 

The  nature  of  sound.  The  production  of  sound.  The  range  of 
the  number  of  vibrations  in  the  production  of  sound.  The 
transmission  of  sound  in  the  air  and  its  velocity  in  the  same. 
Reflection  and  refraction  of  sound.  The  physical  proper- 
ties of  sound.  Harmony.  Sympathetic  vibrations.  The 
external  ear.  The  middle  ear.  The  membranous  ear. 
Histology  of  the  membranous  labyrinth.  The  minute  struc- 
ture of  the  membranous  cochlea.  The  functions  of  the  in- 
dividual parts  of  the  membranous  ear.  The  localization  of 
sound 494 


CHAPTER    XXIII. 
The  Eye  and  the  Physiology  of  Vision. 

Historical.  The  nature  of  light.  The  rate  of  transmission.  The 
number  of  vibrations  in  waves  of  light.  The  spectrum. 
Complementary  colors.  The  colors  of  objects  by  transmitted 
or  reflected  light.  The  refraction  of  light  and  the  property 
of  lenses.  The  formation  of  images  by  lenses.  The  anat- 
omy of  the  eye  (eyebrows,  eyelids,  lachrymal  apparatus, 
muscles  of  the  eyeball,  the  globe  of  the  eye,  sclerotic  coat, 
choroid  coat,  ciliary  muscles  and  the  muscles  of  accomoda- 


X  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

tion,  optic  nerves,  microscopic  structure  of  the  retina).  The 
eye  as  a  purely  physical  instrument.  The  normal  or  emme- 
tropic  eye  (myopia,  hypermetropia,  astigmatism,  cataract, 
spherical  aberration,  chromatic  aberration,  muscae-voUtan- 
tes,  presbyopia) .  The  manipulation  of  the  eye  as  an  opti- 
cal instrument.  How  do  we  focus  the  eye?  The  dioptrics 
of  the  eye.  The  luminosity  of  eyes.  The  physiology  of 
color  sensation.  Color  blindness.  The  Young-Helmholtz 
theory.  Normal  or  trichromatic  eyes.  The  Hering  theory. 
After-images.  Explanation  of  negative  after-images. 
Double  vision.  The  advantages  of  two  eyes.  Optical  illu- 
sions . .  529 


INTRODUCTION. 

What  are  the  reasons  that  entitle  the  subject  of  physiol- 
ogy to  a  place  in  the  common  school  curriculum?  There 
are  now  so  many  subjects,  on  the  educational  value  of 
which  most  educators  are  agreed,  that  unless  physiology 
can  do  for  the  student  what  these  do,  it  ought  to  give  way 
to  better  fields  of  study. 

In  many  cases  no  doubt  it  is  taught  simply  because  it  is 
prescribed  by  law,  and  its  injunctions  are  not  questioned. 
In  other  cases  its  study  is  considered  desirable,  or  even 
necessary,  because  physiology  concerns  itself  so  largely 
with  hygienic  considerations,  and  so  is  believed  to  exert  a 
helpful  influence  on  the  general  health.  Possibly  this  is 
the  main  purpose  our  legislators  had  in  mind  when,  by 
statute,  physiology  was  made  one  of  the  common  school 
branches.  No  one  will  deny  the  value,  in  fact  the  neces- 
sity, of  having  clear  conceptions  of  hygienic  rules  and 
thoroughly  understanding  the  laws  of  sanitation.  It  is  the 
author's  firm  belief  that  if  the  knowledge  of  the  nature  of 
contagious  and  infectious  diseases  and  of  the  means  of 
their  spreading,  was  more  generally  possessed,  perfected 
sanitation  would  be  declared  a  necessity,  and  the  public 
health  would  be  greatly  improved.  Such  a  result  would 
repay  a  thousand  times  the  cost  of  teaching  such  practical 
information.  It  is  however  a  question  whether  it  usually 
pays  to  have  the  study  of  physiology  degenerate  into  formal 
rules  of  health,  and  recipes  for  disease.  Such  formal, 
theoretical  knowledge  seldom  becomes  of  practical  benefit. 
Most  of  us  eat  what  our  pocketbooks  can  afford  and  what 
experience  shows  agrees  with  us.  We  regulate  our  exer- 
cise by  the  amount  of  time  available,  and  our  inclination  to 
take  it.  The  desirability  of  bathing  arises  from  something 
deeper  than  a  mere  intellectual  perception  of  its  value. 

(i) 


2  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

The  tramp  probably  possesses,  in  some  instances,  a  theoret- 
ical knowledge  of  the  efficacy  of  soap  and  water,  but  it 
does  not  therefore  become  a  practical  belief. 

In  teaching  small  children  it  is  of  course  desirable  to 
make  almost  all  the  work  of  this  hygienic  character. 
Physiology  is  a  science  that  pre-supposes  some  knowledge 
of  physics  and  chemistry,  and  that  cannot  be  assumed  in 
really  elementary  classes.  In  addition  small  children  have 
a  morbid  curiosity  aroused  when  dealing  with  anatomical 
structures  that  is  frequently  productive  of  more  evil  than 
good.  But  with  advanced  classes  physiology  can  be  studied 
to  the  greatest  advantage,  provided  that  we  do  so  in  a 
scientific  way.  While  in  a  strict  sense  physiology  does  not 
at  all  include  anatomy,  either  gross  or  minute,  yet  as  gen- 
erally conceived  it  is  made  to  include  this,  and  in  such  a 
sense  it  is  used  by  the  author.  While  pure  physiology  is 
a  science  of  experiments,  like  physics  and  chemistry,  and 
not  a  science  of  observation  like  botany  and  zoology,  and 
as  from  the  difficulty  of  the  experiments,  not  many  of  them 
can  be  repeated  by  the  student  himself,  yet  there  are 
numerous  simpler  experiments  of  deepest  physiological 
import  which  the  student  can  perform  for  himself.  Some 
experiments  in  artificial  digestion  with  prepared  extracts, 
the  nature  of  the  flow  of  liquids  in  iron  and  rubber  tubes  to 
illustrate  circulation,  the  phenomena  of  blood  coagulation, 
and  finally  the  many  experiments  to  be  made  in  the  study 
of  the  special  senses,  all  these  will  afford  abundant  oppor- 
tunities to  perform  experiments  of  the  highest  educational 
value.  But  it  is  when  we  include  anatomy  that  the  oppor- 
tunities are  greatest.  It  is  never  necessary  in  elementary 
instruction  to  call  to  aid  vivisections,  or  even  ordinary 
dissections  of  a  nature  often  calculated  to  be  repulsive. 
Let  all  these  be  proscribed.  But  the  meat  market  itself 
will  afford  a  multiplicity  of  material  which  will  serve 
to  illustrate  all  the  more  important  fields  of  anatomy. 
Now  it  is  believed  that  while  a  large  part  of  the  matter  of 
physiology  must  be  informational,  and  although  this  is  often 


INTRODUCTION.  3 

of  the  greatest  value,  the  best  thing  this  subject  can  do  for 
the  student  is  to  allow  him  to  make  his  own  observations  as 
far  as  possible,  and  to  make  his  own  interpretations  of 
experiments  from  related  facts  out  of  his  own  experience. 
There  is  not  so  much  educational  value  in  knowing  that  the 
heart  possesses  auricles,  ventricles  and  valves,  as  there  is 
in  finding  and  understanding  them  when  a  real  heart  is  being 
examined.  There  is  an  endless  difference  in  mental  value 
between  learning  a  few  curious  things  about  the  brain  from 
the  book  or  a  cheap  model,  or  even  the  description  of  a 
teacher,  and  in  studying  for  ourselves,  in  detail,  the  varied 
anatomy  of  a  real  sheep's  brain.  One  leaves  us  with  hazy 
and  dim  ideas,  the  only  real,  tangible  thing  of  which  are  the 
words  to  symbolize  them,  but  the  other  results  in  real, 
definite,  and  lasting  information.  To  have  dissected  out  the 
salivary  glands  on  the  sheep's  head,  furnished  by  the  meat 
market ;  to  have  seen  the  Eustachian  tube ;  to  have  cut  out 
the  tonsils ;  observed  the  large  circumvallate  papillae  on  the 
tongue  ;  to  have  seen  the  lens  and  separated  the  coats  of  the 
eye ;  to  have  hunted  for  and  found  the  middle  ear  with  its 
chain  of  bones,  possibly  to  have  laid  open  the  cochlea;  to 
have  seen  all  these  things  on  a  single  sheep's  head,  will  be 
of  more  lasting  benefit  and  real  educational  worth  than  the 
ability  to  repeat  from  memory  a  chapter  at  a  time  of  the 
latest  edition  of  Quain's  Anatomy.  If,  to  carry  the  sug- 
gestion a  little  further,  the  student  could  observe  and  study 
with  his  own  eyes  the  sympathetic  system  as  it  hangs  dis- 
played in  every  meat  market,  if  he  could  but  see  one 
ganglion,  one  nerve  trunk,  and  really  learn  to  know  it,  if 
he  could  grasp  with  the  fingers  of  his  hand  as  well  as  those 
of  his  mind  a  single  typical  gland,  crush  with  his  thumb  but 
one  lymphatic  nodule  to  know  it,  if  in  short  he  could  get 
a  living  knowledge  of  the  more  important  structures  alone, 
he  would  not  only  have  acquired  facts  which  are  indelible 
and  can  be  turned  to  practical  advantage,  but  he  will  have 
acquired  a  discipline  in  their  acquisition  which  will  give 
added  power  to  the  entire  mind.  Furthermore,  and  possibly 


4  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

best  of  all,  he  is  acquiring  new  facts  in  the  way  lie  will  be 
obliged  to  acquire  them  when  he  leaves  the  school,  and 
when  there  will  no  longer  be  a  teacher  to  diagram  every 
difficulty  on  the  board  in  colored  crayons,  and  when  the 
student  will  no  longer  be  carried  each  day  ' '  three  pages  in 
advance." 

By  making  his  own  actual  observations  on  actual  tan- 
gible material  he  is  not  only  training  his  powers  of  observa- 
tion which  are  directly  concerned,  but  by  the  care  required 
to  verify  his  observations,  and  by  strict  reasoning  of  the 
mind  to  properly  interpret  his  observations,  he  is  developing 
all  those  faculties  of  mind  which  are  required  in  the  acqui- 
sition of  any  new  truth.  He  will  learn  what  it  often  costs 
to  make  but  one  point,  he  will  see  what  painstaking  efforts 
it  frequently  requires  to  establish  but  one  new  fact,  and  he 
will  not  be  discouraged  when  later  on  he  finds  it  hard  to 
make  progress.  He  will  know  that  to  learn  but  one  point 
as  it  ought  to  be  learned  is  making  more  real  progress  than 
to  have  many  poured  into  him.  He  will  have  somewhat  of 
a  criterion  by  means  of  which  to  gauge  his  own  pace.  It 
is  certainly  an  attitude  of  mind  brought  about  by  scientific 
study  not  to  accept  too  quickly  what  seems  still  unproved, 
be  it  from  the  assurances  of  the  patent-medicine  quack  to 
the  politician  with  his  latest  schemes  on  finance.  Huxley 
compared  knowledge  with  the  virus  of  vaccination.  When 
the  virus  is  fresh,  when  it  comes  directly  from  its  original 
source,  it  is  wonderfully  potent,  but  passed  through  the 
tissues  of  other  animals  it  is  gradually  weakened  and  may 
finally  have  no  effect  at  all.  So  knowledge  gained  first- 
hand, from  the  objects  themselves,  from  the  experiments 
themselves,  is  wonderfully  potent,  but  passed  through  the 
tissues  of  several  text-books  or  handed  down  through  several 
teachers,  it  is  gradually  weakened  until  finally  when  it  is 
administered  it  is  too  weak  to  save  us  from  the  intellectual 
epidemics  of  the  day. 


CHAPTER  I. 


AN  EPITOME  OF  THE  HISTORY  OF  PHYSIOLOGY. 

The  word  physiology  now  used  to  designate  this  and 
kindred  subjects,  has  a  very  remote  origin.  Etymologi- 
cally  it  means  a  discourse  on  nature,  from  the  Greek  words 
physis  (0"'<H?),  meaning  nature,  whence  the  word  physical, 
and  logos  (?-<w),  meaning  a  discourse.  In  this  original 
sense  it  was  employed  by  the  earliest  writers  to  include  all 
the  natural  sciences.  Soon  astronomy  was  set  off  as  a  spe- 
cial science,  and  the  term  restricted  to  all  subjects  that 
deal  with  natural  phenomena  and  natural  objects  close  at 
hand.  Little  by  little  as  human  knowledge  widened, 
and  the  accumulated  observations  and  experiments  in 
any  one  field  became  considerable,  this  field  was  sepa- 
rated from  the  general  study  of  nature,  physiology,  and 
designated  by  its  own  peculiar  name.  In  this  way  the 
accumulating  facts  in  the  domain  of  chemistry  gave  rise  to 
the  alchemy  of  the  Middle  Ages,  and  when  later  alchemy 
was  stripped  of  its  superstitions  and  fancies,  it  rose  to  the 
dignity  of  the  science  of  chemistry.  Soon  purely  physical 
facts  were  separated  off  as  the  science  of  natural  philosophy 
and  have  become  the  science  of  physics.  This  eliminating 
process  has  continued  with  the  progress  of  science  until  the 
original  term  physiology,  which  means  the  study  of  entire 
nature,  has  been  contracted  so  as  to  apply  only  to  that 
science  which  seeks  to  explain  vital  phenomena,  be  it  in 
plant  or  in  animal. 

Etymologically  physiology  is  the  parent  science  and  all 
others  outgrowths  of  it.  But  not  only  in  an  etymological 
sense  is  physiology  of  early  origin.  While  logically  phys- 
iology follows  physics,  chemistry,  botany  and  zoology,  and 

(5) 


6  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

presupposes  them  at  many  steps,  yet  historically  almost  the 
exact  opposite  is  true.  It  is  a  trait  of  the  human  mind  ap- 
parently to  attack  a  problem  by  attempting  at  once  the 
explanation  of  its  deepest  questions.  Thales,  Anaximan- 
der,  Anaximenes,  Heraclitus  and  other  early  Grecian  phil- 
osophers busied  themselves  with  trying  to  explain  the  ulti- 
mate essence  of  things  before  the  world  had  made  even 
the  first  real  attempt  to  learn  something  of  the  things  them- 
selves. 

HIPPOCRATES. 

Ancient  writers  cite  Hippocrates  of  Macedon  as  the 
person  in  whom  physiological  observations  began.  He  is 
often  called  the  "  Father  of  Medicine."  Hippocrates  was 
a  contemporary  of  Socrates  and  Plato,  and  he  is  especially 
deserving  of  credit  because  he  insisted  that  the  proper  way 
to  study  disease  and  health  was  by  observation  and  experi- 
ment, and  not  by  the  application  of  general  deductions. 
He  antedated  Bacon  many  centuries  in  trying  to  establish 
the  inductive  method  of  scientific  investigation.  While 
Hippocrates  added  but  little  to  the  physiological  con- 
ceptions of  his  times,  he  described  numerous  phenomena 
with  great  care,  and  made  observations  and  experiments 
which  made  him  the  foremost  physician  of  his  time.  We 
still  speak  of  the  Hippocratic  face  after  death,  of  the 
Hippocratic  sleeve  for  straining  syrups  and  decoctions,  and 
in  our  drug  stores  may  still  be  bought  the  wine  of  Hippo- 
crates, supposed  to  be  made  after  the  formula  of  that  early 
physician. 

AEISTOTLE. 

But  while  Hippocrates  has  possibly  the  honor  of  being 
the  first  scientific  physician,  the  honor  of  being  the  first  to 
study  physiology  scientifically  belongs  to'  Aristotle,  often 
called  the  "Father  of  the  Sciences."  True  it  is  that 
Aristotle  laid  down  many  of  the  fundamental  conceptions 
of  our  sciences  of  to-day.  One  is  astonished  at  his  general 
knowledge,  and  in  many  cases  the  careful  investigations  of 


HISTORY   OF    PHYSIOLOGY.  7 

later  times  have  shown  the  accuracy  of  his  observations  on 
points  which  at  first  seemed  mere  fancies  of  his  mind.  He 
wrote  several  works  on  physiological  matters.  His  works 
entitled,  "  Natural  History  of  Animals,"  "  On  the  Parts  of 
Animals,"  on  "Animal  Locomotion,"  "On  Respiration," 
are  in  part  preserved,  while  a  treatise  on  anatomy  seems  to 
have  been  lost.  From  these  writings  the  views  of  his 
time  are  accessible.  The  main  purpose  with  Aristotle 
was  to  explain  the  function  of  every  part  and  organ 
described.  Some  of  the  main  conceptions  of  Aristotle  are 
here  briefly  given: — The  heart  is  the  central  organ,  and 
the  motive  power  of  the  whole  body.  It  is  the  seat  of 
vitality,  because  it  is  the  source  of  the  animal  heat  of  the 
body,  all  the  warmth  of  the  body  being  produced  by  the 
heart.  The  heart  makes  the  blood,  gives  to  it  its  vital  stimu- 
lus, and  then  sends  it  all  over  the  body  through  the  blood 
vessels.  The  blood  does  not  circulate,  it  never  returns  to 
the  heart,  but  as  fast  as  it  is  used  up  at  the  periphery  of 
the  body  it  is  replaced  in  the  heart.  The  blood  is  stored 
in  the  blood  vessels  as  in  a  jar.  Whence  the  name  blood 
vessel  used  to  this  day.  (The  name  "aorta"  dates  from 
Aristotle.)  Aristotle  describes  the  stomach  and  intestines, 
and  hints  at  the  proper  conception  of  absorption.  He 
describes  the  trachea  by  the  name  artery,  and  says  that  it 
carries  air  into  the  lungs.  In  the  lungs  the  spiritus  or 
pneuma  is  extracted  from  the  air  and  by  channels  (pul- 
monary artery  and  veins,  no  doubt  referred  to)  this 
"spirit"  substance  is  carried  to  the  heart,  where  it  is 
mixed  by  the  heart  with  the  blood,  and  serves  to  give  it 
its  vital  stimulus.  The  ancient  notion  that  the  air  or 
' '  spiritus  ' '  is  the  vital  principle  still  lingers  in  our  every- 
day language  when  we  refer  to  vital  things  as  spiritual,  or 
call  the  active  element  of  wine  spirits,  although  now  hav- 
ing an  entirely  different  meaning.  Aristotle  explains  all 
vital  processes  as  caused  by  lieat.  Heat  was  the  "causa 
operandi "  for  everything.  "Heat  changes  the  metals, 
disintegrates  ores,  liquids,  and  then  vaporizes  ice,  causes 


8  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

the  embryo  to  grow  in  the  egg;  in  short,  heat  causes  all 
the  processes  of  life."  "But  this  heat  must  not  go  too 
high,  and  so  we  have  respiration,  which  enables  us  to 
breathe  in  cold  air  and  so  cool  the  blood.  For  this  reason 
we  breathe  the  faster  the  hotter  we  are ! ' ' 

While  much  of  Aristotle's  information  is  remarkably 
exact  when  we  remember  his  times,  and  shows  him  to  have 
been  a  scientist  such  as  the  world  has  rarely  seen  since,  yet 
here  and  there  we  find  ideas  that  seem  somewhat  puerile. 
Thus  he  says  with  great  earnestness  "that  in  all  his  dissec- 
tions, and  he  has  made  many,  he  has  always  found  the 
windpipe  leading  to  the  lungs  and  the  oesophagus  to  the 
stomach,  nor  has  he  ever  found  them  interchanged." 

PRAXAGORAS. 

The  views  of  Aristotle  were  extended  by  Praxagoras, 
whose  important  addition  to  physiological  knowledge  was 
the  distinction  he  found  between  arteries  and  veins.  He 
also  noticed  the  pulsations  of  the  arteries  and  the  absence 
of  a  pulse  from  the  veins.  This  was  a  material  gain.  But 
with  this  discovery  there  crept  in  a  misconception  which 
remained  for  centuries  and  formed  the  fundamental  con- 
ception of  all  the  earlier  physiologists.  This  was  that  the 
veins  are  filled  by,  and  carry  the  blood,  but  that  the  arteries 
have  no  liquid  of  any  kind  in  them,  but  carry  the  mysterious 
"spiritus"  or  "pneuma,"  something  akin  but  not  exactly 
the  same  as  ordinary  air.  This  misconception  arose  no 
doubt  from  the  observation  that  after  death  the  arteries  are 
empty  and  all  the  blood  practically  is  found  in  the  veins. 
The  word  artery,  arteria,  was  used  by  Aristotle  for  the 
trachea,  as  it  was  clearly  an  air- tube,  but  was  by  Praxagoras 
applied  to  the  pulsating  blood-vessels  under  the  idea  that 
they  too  contained  air.  We  still  use  the  name  artery, 
although  since  the  time  of  Galen  we  know  that  they  carry 
blood  and  not  air.  None  of  the  works  of  Praxagoras  are 
preserved,  but  his  views  are  quoted  by  later  writers. 


HISTORY    OF    PHYSIOLOGY.  9 

HEEOPHILU8  AND  THE  ALEXANDRIANS. 

Praxagoras  had  for  his  pupil  the  anatomist  Herophilus, 
whose  influence  contributed  to  the  renown  of  the  school  at 
Alexandria,  whose  greatest  achievements  were  in  the  realm 
of  anatomy,  physiology  and  medicine.  The  great  Alexan- 
drian museum  became  the  center  of  learning  of  the  ancient 
world.  Scholars  from  all  parts  of  the  world  gathered  there 
to  prosecute  their  studies.  The  attendance  is  given  by 
some  writers  as  having  reached  10,000  students  at  one 
time.  A  glance  at  some  of  the  names  will  convince  one  of 
the  pre-eminence  of  this  first  great  university  of  the  world. 
Here  Euclid  wrote  his  geometry,  here  Ptolemy  worked  out 
the  "Ptolemaic"  astronomy,  Archimedes  his  physics. 
Here  originated  the  theological  disputes  between  Arius  and 
Athanasius  which  culminated  in  the  Nicene  creed.  Here 
the  dissection  of  the  human  body  was  allowed  by  law,  and 
the  bodies  of  condemned  criminals  were  turned  over  to  the 
students  of  anatomy.  Here  the  anatomists,  Herophilus  and 
Hrasistratus,  were  the  first  "professors  of  anatomy"  in  a 
public  institution.  Many  anatomical  structures  were  here 
first  described  and  still  bear  their  ancient  names,  the  tri- 
cuspid  valves  of  the  heart,  the  duodenum,  the  calamus 
scriptorius,  etc.  Erasistratus  distinguished  between  con- 
nective tissue  cords  and  true  nerves,  and  even  distin- 
guished between  sensory  and  motor  nerves. 

A  marvelous  advance  was  made  by  Herophilus  in  the 
conceptions  of  brain  and  spinal  cord.  By  earlier  writers 
they  were  regarded  as  unimportant  collections  of  fat-like 
tissues  something  like  the  marrow  of  the  bones.  The  fact 
that  the  earlier  observers  could  see  nothing  in  these  struc- 
tures except  a  soft  structureless  mass  led  to  this  error.  The 
term  "spinal  marrow"  still  used  is  probably  a  relic  of  the 
times  when  this  organ  was  not  understood.  Herophilus 
made  the  brain  the  seat  of  conscious  activities;  the  center 
to  which  sensations  are  carried  and  the  sourcs  of  voluntary 
movements.  What  a  step  forward  in  the  field  of  physio- 
logical research !  But  with  all  these  advances  they  never 


10  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

doubted  the  truth  of  the  conceptions  of  Praxagoras  regard- 
ing the  arteries.  They  were  in  all  calculations  supposed  to 
to  carry  air  or  spuitus.  This  spirit  us  or  pncuma  they 
made  the  subject  of  many  fanciful  theories.  It  was  still 
believed  to  be  taken  in  by  the  breath  and  then  carried  to 
the  heart,  to  be  distributed  by  the  arteries.  It  was  the 
principle  of  life,  and  we  have  the  ancient  belief  still  illus- 
trated in  the  familiar  expression  "the  breath  of  life." 

This  spiritus  by  its  vital  energy  caused  the  arteries  to 
pulsate.  Brasistratus  carried  this  notion  so  far  as  to  rec- 
ognize two  kinds  of  spiritus.  One  which  was  taken  from 
the  air  is  carried  in  the  arteries  and  left  side  of  heart,  and 
the  other  a  higher  spiritus  made  from  the  first  by  the  brain 
and  stored  in  the  ventricles  of  the  brain  (whence  their 
use) ,  from  there  to  be  distributed  over  the  body  by  the 
nerves  giving  feeling  and  volition,  while  the  part  that 
remained  in  the  brain  became  the  bearer  of  consciousness 
and  individuality.  This  was  called  the  "psyche,"  a  name 
retained  to  this  day  in  such  terms  as  psychical,  psychology, 
etc.,  while  we  still  speak  of  animal  spirits,  and  sometimes 
hear  of  the  nerves  containing  nervous  flttid.  Fever  was 
believed  to  be  due  to  the  filling  of  the  large  arteries  with 
blood  and  so  interfering  with  the  movements  of  the  pneuma, 
while  inflammation  resulted  when  the  blood  was  driven  by 
the  pneuma  to  the  ends  of  the  arteries,  whence  their  dis- 
tension. In  a  wound  the  artery  contained  blood,  because 
as  the  air,  or  pneuma,  leaked  out  and  so  caused  a  vacuum, 
blood  soaked  in  to  take  its  place.  Normally  blood  was 
contained  in  veins  only. 

GALEN. 

The  physiology  of  the  ancients  reached  its  culminating 
point  in  the  learned  Galen,  who  practiced  medicine  in  the 
city  of  Rome  when  the  Eternal  City  had  reached  the  zenith 
of  its  importance.  He  was  a  Grecian  by  birth  and  no  doubt 
belonged  to  that  class  of  Greeks  which  had  been  called  to 
Rome  to  superintend  the  instruction  of  the  imperial  city. 


HISTORY    OF    PHYSIOLOGY.  11 

Galen  was  the  medical  adviser  of  the  imperial  family  itself 
and  so  probably  the  most  learned  physician  of  Rome.  It 
is  due  to  the  genius  of  Galen  to  have  put  an  end  to  some 
of  the  misconceptions  clustering  around  the  idea  of  the 
pneuma  and  the  arteries.  He  established  the  fact  that  the 
arteries  normally  contain  blood.  He  describes  that  having 
laid  bare  the  axillary  artery  of  an  animal  while  it  was  pul- 
sating regularly,  and  so  according  to  the  established  notion 
containing  pneuma,  he  pricked  it  with  a  fine  needle,  and 
found  that  in  the  very  first  instance  blood  came  out,  and 
TLO\.  pneuma,  followed  later  by  blood,  which  had  soaked  in. 
When  such  a  pulsating  artery  was  cut  the  blood  spurted 
out  forcibly  at  once,  showing  that  it  must  have  contained 
blood  before  opening.  What  a  simple  and  conclusive  exper- 
iment !  and  yet  it  had  taken  the  world  centuries  to  think  of 
it.  He  also  described  the  heart  very  carefully,  and  even 
investigated  successfully  the  changes  in  the  circulation  at 
birth,  having  found  the  foramen  ovale  and  the  duct  of 
Botallus  (duct us  arteriosus] ,  and  noted  tke  closing  of  the 
former  and  the  atrophy  of  the  latter.  (See  chapter  on 
"Changes  of  the  Circulation  at  Birth.")  The  discovery 
of  the  true  blood-carrying  function  of  the  arteries  was 
another  tremendous  step  in  the  right  direction,  but  in  trying 
to  work  out  his  idea  of  the  system  of  blood  vessels  Galen  was 
led  into  several  new  misconceptions.  From  an  historical 
standpoint,  however,  they  are  of  peculiar  interest.  Galen 
made  the  liver  the  seat  of  the  elaboration  of  the  blood. 
The  portal  circulation  carries  the  foods  from  the  stomach 
and  intestines  to  the  liver  (and  in  this  he  was  correct)  and 
by  the  liver  this  food  material  was  transformed  into  blood. 
From  the  liver  two  vessels  arose,  one  running  downward  to 
the  lower  part  of  the  trunk,  and  lower  extremities ;  the  other 
running  upward  to  the  heart.  (In  this  way  he  had  inter- 
preted the  large  vena  cava  running  through  the  liver  to  the 
heart.)  Through  the  right  side  of  the  heart  the  ascending 
vessel  was  extended  to  the  head  and  upper  part  of  the  body 
(our  descending  vena  cava  and  innominate  veins)  and 


12  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

through  the  ventricle  of  the  heart  to  the  lungs  (our  pulmo- 
nary artery) .  This  system  he  called  the  venous  system  and 
the  blood  venous  blood.  This  venous  blood  was  dark,  being 
rich  in  nutritive  matter  and  intended  to  give  to  all  the 
organs  to  which  it  was  distributed  the  proper  substantial 
nourishing  matters.  On  the  left  side  of  the  heart  and  in 
the  arteries  there  was  an  entirely  different  kind  of  blood, 
and  having  no  connection  in  any  way  writh  the  other  or 
venous  blood.  This  blood  he  termed  the  arterial  blood. 
It  was  lighter  in  color  and  weight  and  carried  the  vitalizing 
pneuma  dissolved  in  it  which  it  received  in  the  lungs.  It 
also  carried  warmth  to  all  parts  of  the  body,  which  warmth 
was  produced  in  the  left  side  of  the  heart.  Both  kinds  of 
blood  ran  to  all  organs,  so  that  each  organ  could  choose 
whether  it  wanted  the  nutritive,  rich,  thick,  venous  blood, 
or  the  quick,  pulsating,  active  pneuma~conta.inmg  arterial 
blood.  It  was  still  believed  that  the  vitalizing  influence  now 
dissolved  in  the  liquid  blood,  the  pneuma,  caused  the  prop- 
erties of  sensation  and  motion. 

Galen,  however,  adds  a  new  idea  to  explain  the  source 
of  the  arterial  blood.  The  venous  blood  is  elaborated  from 
the  food  carried  to  the  liver  by  the  portal  vein,  but  there 
seemed  at  first  sight  no  way  to  account  for  the  production  of 
the  lighter  arterial  blood.  The  vital  spirits  were  extracted 
from  the  air  and  added  to  it  in  the  lungs,  from  which  place 
the  blood  carried  the  vital  spirits  to  the  left  side  of  the  heart, 
where  the  finishing  touches  were  given  to  it,  and  from  which 
it  was  sent  out  over  the  body.  Galen  solves  this  point  by 
admitting  that  there  are  pores,  very  tiny  ones  though, 
through  the  thick  ventricular  septum,  so  that  the  finer  parts 
of  the  blood  from  the  right  side  could  soak  through  these 
invisible  openings  to  the  left  side.  Further  he  contended, 
and  this  seems  remarkable  now,  that  the  arteries  and  veins 
anastomose  with  each  other  at  their  outer  ends  by  means  of 
excessively  fine  sieve-like  canals  and  pores,  so  that  again 
some  of  the  lighter  parts  of  the  venous  blood  could  gradually 
soak  into  the  arterial  svstem,  and  so  replenish  the  arterial 


HISTORY   OF   PHYSIOLOGY.  13 

blood  as  it  was  used  up.  This  view  Galen  supported  by  the 
observed  fact  that  when  an  artery  of  an  animal  was  cut,  not 
only  the  arteries,  but  the  veins,  also,  became  emptied  in  a 
very  short  time. 

Middle  Ages. 

With  Galen  the  progress  of  the  ancients  in  physiology 
conies  to  a  close.  A  thousand  years  have  elapsed  before 
physiological  phenomena  receive  the  least  attention,  and 
nonsensical  metaphysical  debates  on  theological  abstrac- 
tions crowd  out  of  the  mind  of  the  Middle  Ages  even  the 
known  conceptions  of  the  past.  Miracle  cures  replaced 
the  medicines  of  Galen  and  Hippocrates,  and  superstition 
gave  way  to  the  anatomy  of  the  ancients.  More  than  ten 
centuries  separate  Galen  from  the  first  students  of  anatomy 
in  the  universities  of  Italy.  But  the  Middle  Ages  had  car- 
ried the  seeds  of  physiology  through  these  years  of  read- 
justment, and  when  the  Italian  Renaissance  came,  anatom- 
ical and  physiological  studies  felt  the  mental  awakening. 
For  the  first  time  in  modern  history,  lectures  on,  and  dis- 
sections of  the  human  body  formed  a  part  of  the  regular 
program  of  studies  of  the  universities.  Mondini  of  Bologna, 
1315,  wrote  a  treatise  on  anatomy  and  dissection  which 
remained  the  authorized  text-book  in  most  schools  of  med- 
icine almost  into  the  sixteenth  century.  Only  twelve  years 
after  the  invention  of  printing  this  treatise  was  printed 
in  full,  and  by  the  year  1550  it  had  no  less  than  thirteen 
editions. 

The  anatomy  of  the  body  is  in  many  instances  carefully 
described,  and  the  chief  value  of  the  book  is  from  an 
anatomical  standpoint.  In  his  physiological  views  the 
established  notions  are  not  questioned.  During  the  Renais- 
sance the  works  of  the  ancients  were  seen  to  be  so  much 
better  than  their  present  productions  that  practically  implicit 
confidence  was  given  to  all  things  that  had  the  authority 
of  the  past.  Aristotle  and  Galen  were  not  to  be  ques- 
tioned, and  it  seemed  senseless  and  unpardonable  to  try  to 


14  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

improve  on  what  they  said,  and  useless  to  try  to  add 
materially  to  their  knowledge.  Galen's  views  of  the  vital 
spirits  and  the  circulation  are  accepted.  Mondini  adds  his 
interpretation  of  the  meaning  of  the  auricles.  They  are 
to  act  as  overflow  reservoirs  for  the  ventricles,  to  store  the 
excess  of  blood  or  vital  spirits  when  the  ventricle  is  manu- 
facturing these  too  rapidly. 

Two  hundred  years  later,  in  1514,  the  chair  of  anatomy 
and  physiology  at  Bologna  was  occupied  by  the  surgeon, 
Carpi,  who  published  a  treatise  on  anatomy  even  more 
extensive  than  that  of  Mondini,  but  not  differing  from  his 
predecessor  in  any  of  his  fundamental  physiological  con- 
ceptions. 

VESALIUS. 

A  new  era  in  physiology  was  ushered  in  by  the  Dutch 
anatomist,  Vesalius,  1537,  whose  immense  credit  lies  not 
so  much  in  what  he  himself  contributed  to  the  science  of 
physiology  as  in  the  position  he  took  with  reference  to  the 
ideas  of  the  past.  He  boldly  antagonized  many  of  Galen's 
views,  showed  that  many  of  his  observations  had  been  con- 
ducted on  animals  and  not  on  the  human  body  itself,  and  so 
recognized  the  necessity  for  more  definite  descriptions. 
With  Vesalius  the  absolute  charm  of  the  all-sufficiency  of 
the  past  was  broken,  and  he  strongly  suggested  the  neces- 
sity of  beginning  anew  the  investigations  of  anatomy  and 
physiology,  and  the  subjection  of  the  ideas  of  the  ancients  to 
a  careful  and  impartial  test.  He  boldly  denied  that  there  are 
pores  through  the  ventricular  septum  as  Galen  describes, 
and  insisted  that  the  traditional  view  of  the  blood  circula- 
tion was  wholly  inadequate  to  explain  all  the  facts,  and  he 
might  have  discovered  the  circulation  of  the  blood  had  he 
remained  the  professor  of  anatomy  at  Padua  and  not  been 
made  court  physician  at  Madrid. 

*/•:/?  FETUS. 

The  next  great  step  forward  in  physiology  came  from  an 
unexpected  source  and  in  a  remarkable  manner.  The  far- 


HISTORY   OF    PHYSIOLOGY.  15 

reaching  statement  that  the  blood  passes  from  the  right  side 
of  the  heart  through  the  lungs,  and  by  means  of  anastomos- 
ing connections  is  transferred  to  the  pulmonary  vein  and  so 
returned  to  the  left  side  of  the  heart,  was  made  by  the 
Spanish  theologian,  Servetus.  Serve tus  wrote  a  number  of 
speculative  treatises  on  theological  disputes,  which  were 
condemned  as  heterodox  by  both  the  Catholic  church  and 
by  Protestants.  After  the  publication  of  his  book,  the 
Errors  of  the  Trinity,  he  was  obliged  to  leave  his  home, 
and  under  an  assumed  name  entered  the  university  of  Paris, 
and  studied  medicine.  But  even  in  the  field  of  medicine 
he  was  considered  as  little  orthodox  as  he  was  in  his  theo- 
logical views,  and  he  was  compelled  to  withdraw  one  of  his 
medical  publications  by  order  of  the  Medical  Council. 

After  drifting  around  for  some  time  as  a  practicing  phy- 
sician he  decided  to  publish  a  book  which  should  set  forth 
his  theological  views  in  detail.  Soon  afterwards  appeared 
his  book  entitled,  the  Restoration  of  Christianity.  In 
explaining  in  this  book  the  workings  of  the  Holy  Spirit,  he 
adds  an  exposition  of  the  vital  spirit  of  the  human  body. 
In  this  exposition  he  says  that  the  blood  goes  to  the  lungs 
from  the  right  side  of  the  heart,  assumes  a  bright  color  in 
tlie  lungs,  and  is  then  transferred  to  the  pulmonary  vein. 
Here  it  is  mingled  with  the  inspired  air,  is  relieved  of  some 
waste  products,  and  then  returns  to  the  heart,  where  the 
u  vital  spirit  "  is  made  out  of  the  arterial  blood.  Hence 
the  soul  resides  in  the  blood  and  not  in  the  solid  organs. 
This  soul  is  nourished  from  the  inspired  air  and  the  finest 
constituents  of  the  blood.  "It,  the  soul,  is  a  thin  spirit 
elaborated  by  the  power  of  heat,  of  a  bright  golden  hue 
and  fiery  potency,  containing  in  itself  the  substance  of 
water,  air  and  fire.  The  very  mind  itself,  the  highest 
form  of  the  soul,  resides  in  the  choroid  plexus  of  the 
ventricles  of  the  brain.  (The  choroid  plexus  is  a  network 
of  blood  vessels  lining  the  ventricles  of  the  brain.)  The 
hollow  ventricles  of  the  brain  are  to  permit  air  to  be  drawn 
through  the  nose  and  ethmoid  bone,  and  stored  up  in  them, 


16  STUDIES    IN  ADVANCED    PHYSIOLOGY. 

so  as  to  renew  the  spirit  in  the  adjacent  blood  vessels  and 
to  ventilate  the  mind.  However,  in  the  abysses  of  these 
ventricles  evil  spirits  often  hide  which  make  war  upon  our 
own  spirit,  and  which  are  not  put  to  flight  until  the  assist- 
ance of  the  Holy  Spirit  is  invoked.  While  consciousness 
resides  in  the  choroid  plexus,  faith  resides  in  the  heart, 
because  as  faith  is  a  fundamental  virtue  it  resides  where  the 
vital  spirit  is  originally  made."  Strange  that  with  such  a 
medley  of  beliefs,  some  of  which  seem  to  border  on  the 
blasphemous  in  their  material  conceptions  of  the  Holy 
Spirit,  there  should  be  included  in  the  plainest  terms  such  a 
wonderful  discovery  as  the  circulation  of  the  blood  through 
the  lungs.  Servetus's  book  was  at  once  seized  as  heretical, 
and  poor  Servetus,  surrounded  by  all  the  copies  of  his  book 
that  could  be  found,  was  burned  at  the  stake  in  1553.  Two 
of  these  original  books  still  exist,  one  at  Paris  and  the 
other  at  Vienna. 

FABEIC1US. 

The  anatomists,  Falloppius  (whence  the  name  Fal- 
loppian  tubes) ,  Botallus  (duct  of  Botallus) ,  Varolius 
(pons  varolii) ,  Eustachius  (Eustachian  tube),  and  others, 
whose  names  are  familiar  to  us  from  anatomical  struc- 
tures that  still  bear  their  name,  added  to  the  science 
of  anatomy  rather  than  physiology.  However,  in  1574 
another  important  step  forward  was  made  by  Fabricius,  in 
the  remarkable  discovery  that  the  veins  normally  possess 
valves.  As  it  was  found  that  these  valves  all  opened 
towards  the  heart,  it  seems  almost  impossible  that  Fabri- 
cius should  not  have  stumbled  upon  the  fact  of  the  circu- 
lation of  the  blood  as  we  know  it  to-day.  But  Fabricius 
made  the  blood  flow  from  the  heart  outwards,  against  the 
valves,  and  he  explained  the  valves,  by  saying  that  they 
prevented  the  too  rapid  flow  from  the  heart  to  the  organs. 
When  there  was  danger  of  congesting  the  organs,  the 
valves  tended  to  close  and  so  shut  off  more  or  less  com- 
pletely the  supply  of  blood  to  that  organ.  The  idea  of  the 
( (  vital  spirits  ' '  taken  in  at  the  lungs  was  still  unques- 


HISTORY   OF    PHYSIOLOGY.  17 

tioned,  but  there  was  laid  additional  emphasis  on  the 
further  idea  that  respiration  was  intended  to  cool  or 
refrigerate  the  blood,  and  the  increased  breathing,  follow- 
ing heavy  exercise  and  the  consequent  rise  in  bodily  tem- 
perature, seemed  in  this  view  amply  explained. 

Modern  Physiology. 

HARVEY. 

The  real  Renaissance  of  physiology  dates  from  the  cel- 
ebrated name  of  William  Harvey,  a  lecturer  in  anatomy  in 
the  College  of  Physicians  in  L,ondon.  To  him  we  are 
indebted  for  the  discovery  of  the  circulation  of  the  blood, 
as  we  now  understand  it.  With  this  discovery  a  myriad  of 
older  conceptions  were  forever  swept  away,  and  the  founda- 
tion laid  for  a  real  scientific  study  of  physiological  phe- 
nomena. Harvey  was  convinced  that  the  older  views  con- 
cerning the  heart  were  wrong.  He  was  an  indefatigable 
experimenter,  and  was  sure  from  his  observations  on  the 
living  heart  that  it  was  nothing  more  than  a  pump.  He 
showed  that  the  veins  carried  blood  to  the  heart,  for  when 
he  tied  the  veins  the  portion  next  the  heart  became  empty 
and  soon  the  heart  itself  was  empty,  while  the  vein  beyond 
the  ligature  was  distended  with  accumulating  blood.  As 
soon  as  he  removed  the  ligature  from  the  veins  the  dis- 
tended portions  emptied  themselves,  the  veins  became  filled 
near  the  heart,  and  the  heart  itself  was  distended.  If,  on 
the  other  hand,  he  ligatured  an  artery  the  portion  next  to 
the  heart  became  largely  swollen,  the  blood  was  gorged  in 
the  distended  heart,  while  the  artery  away  from  the  ligature 
gradually  emptied  itself.  Now,  when  the  ligature  was  re- 
moved the  heart  emptied  the  blood  into  the  relieved  artery 
at  once.  Nothing  could  be  clearer.  Harvey  explained  the 
function  of  auricles  and  fairly  accurately  described  the  phe- 
nomena of  the  heart's  beat. 

This  remarkable  discovery  was  published  in  the  year 
1628,  which  date  may  be  considered  the  beginning  of  Mod- 
ern physiology,  and  the  close  of  its  "Middle  Ages."  The 


18  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

book  was  written  in  Latin,  as  was  usual  in  those  times,  and 
is  called  Exercitatio  Anatomica  de  Motui  Cordis  et  San- 
guinis  in  Animalibus.  A  copy  of  this  original  edition  is 
now  in  the  Astor  Library  in  New  York.  It  seems  curious, 
however,  that  Harvey  should  not  have  believed  in  a  direct 
anastomosing  of  the  arteries  and  veins.  Such  a  notion  had 
been  advanced  by  former  anatomists,  and  it  seems  but  nat- 
ural that  Harvey  should  at  once  have  accepted  this  view  to 
explain  the  translation  of  the  blood  from  the  arteries  to  the 
veins,  the  only  missing  point  to  establish  his  discovery. 
Just  how  the  translation  is  effected  Harvey  was  unable  to 
answer. 

Harvey's  discovery  made  a  profound  impression  upon 
the  thinkers  of  his  day.  It  was  a  revolution  in  the  accepted 
doctrines  of  more  than  2,000  years.  It  did  away  with  the 
somewhat  fascinating  "vital  spirits,"  with  the  "moving 
force"  inherent  in  "arterial  blood,"  and  with  the  mystic 
functions  ascribed  to  the  heart  and  lungs.  It  made  the 
heart  a  mere  muscular  pump,  it  explained  all  the  valves  of 
the  heart  and  veins  simply  as  those  of  an  ordinary  water 
pump,  it  explained  the  mysterious  pulse  as  a  mere  wave 
caused  by  the  contraction  of  the  heart  forcing  the  inert 
blood  into  the  arteries,  just  as  would  have  occurred  if  water 
instead  of  blood  had  been  used.  It  did  away  with  the  idea 
of  two  kinds  of  blood,  venous  and  arterial,  and  showed  that 
one  was  changed  into  the  other  in  the  lung  by  being  put  in 
contact  with  the  air.  Men  are  always  slow  to  part  with 
ideas  that  have  the  prestige  of  the  past,  and  so  we  find 
Harvey's  views  at  once  stubbornly  opposed.  The  learned 
physician,  James  Primerose,  wrote  a  lengthy  treatise  oppos- 
ing Harvey's  views  in  which  he  criticises  Harvey  very 
severely  for  taking  "too  great  license  in  impugning  the 
doctrine  of  the  ancients." 

LATER  INVESTIGATORS. 

Harvey's  experiments  were,  however,  so  convincing  that 
it  was  useless  to  question  them,  but  the  authority  of  Galen 


HISTORY    OF    PHYSIOLOGY.  19 

was  still  too  strong  and  several  attempts  were  made  to 
adapt  the  views  of  Harvey  to  the  conceptions  of  Galen. 
Riolan,  the  anatomist  of  the  celebrated  Paris  School,  pub- 
lished his  Circulation  of  the  Blood,  1648,  in  which  he 
tried  to  show  that  Galen  was  correct  in  the  main,  but  that 
a  little,  just  a  little  blood  circulated  from  the  arteries 
through  to  the  veins.  It  did  not,  however,  circulate 
through  the  lungs,  but  the  venous  blood  reached  the  arter- 
ies by  passing  through  the  ventricular  septum.  The  lung 
was  to  furnish  the  " vital  spirits"  as  before  understood. 

Gradually  Harvey's  views  were  adopted,  and  a  new 
epoch  in  physiology  ushered  in.  In  1651  Bartholini  and 
Rudbeck  announced  the  discovery  of  the  system  of  lym- 
phatics, thus  adding  another  chapter  to  the  circulation,  and 
in  1655  the  circulation  of  blood  was  finally  demonstrated  as 
a  fact  by  Marchetti  of  the  University  of  Padua,  who  injected 
a  human  cadaver  and  was  thus  enabled  to  follow  the  trans- 
lation of  the  injected  fluid  through  the  entire  circulation. 

The  capstone  of  the  fact  of  the  circulation  was  finally 
added  by  the  celebrated  physiologist  Malpighi,  of  the  Uni- 
versity of  Bologna,  1661.  It  was  he  who  saw  for  the  first 
time  the  circulation  through  the  capillaries.  He  examined 
with  a  "  magnifier"  the  lung  tissues  of  a  frog,  and  to  his 
surprise  found  the  long  disputed  connections  between  the 
arteries  and  the  veins.  The  discovery  and  description  of 
the  "plexus  of  capillaries"  belong  to  Malpighi.  Soon 
afterwards  with  the  just-invented  microscope,  L,eeuwenhoek 
of  Holland,  the  pioneer  in  microscopy,  discovered  the  "  red 
globules"  circulating  in  the  blood.  By  this  chain  of  dis- 
coveries was  established  one  of  the  most  important  chapters 
in  physiology — the  circulation  of  the  blood. 

A  long  line  of  illustrious  physiologists  has  contributed  its 
discoveries  from  that  time  to  the  present.  The  phenomena  of 
respiration  were  cleared  up  when  Priestly  and  L,avoisier  dis- 
covered oxygen  gas  and  explained  the  nature  of  oxidation. 
Priestly  and  L,avoisier  were  misled,  however,  in  believing 
that  the  lung  was  the  seat  of  the  oxidation  in  the  body, 


20  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

and  that  the  heat  made  here  was  carried  over  the  body  by 
the  blood.  The  important  fact  that  the  oxidation  is  in  the 
tissues  themselves  was  finally  established  by  Liebig  and 
Pfliiger  in  their  study  of  muscular  tissue  in  1867.  The 
nervous  control  and  regulation  of  breathing  studied  first  by 
L,e  Gallois  in  1812  was  extended  by  Flourens  in  1842, 
Traube  1847,  and  Rosenthal  1862.  The  processes  of  secre- 
tion were  also  soon  investigated.  The  notions  of  the  an- 
cients on  this  point  were  very  primitive.  They  regarded  the 
discharge  of  the  mucous  phlegm  from  the  nose  as  an  elim- 
ination from  the  brain  which  soaked  through  the  ethmoid 
bone  into  the  nose.  The  study  of  glands  by  Peyer,  Brun- 
ner  and  Malpighi  soon  established  the  anatomy  of  secretory 
tissues.  The  action  of  nerves  on  glands  was  brought  to 
light  by  the  successful  experiments  of  L,udwig  and  Bernard 
of  our  own  day,  who  succeeded  in  producing  the  salivary 
secretion  by  the  artificial  stimulation  of  the  nerves  going 
to  the  gland.  The  celebrated  physiologist  of  Berlin,  Du 
Bois  Reymond,  brought  to  light  a  multitude  of  observations 
on  the  electrical  properties  of  living  tissues.  To  that  most 
remarkable  scientist,  Helmholtz,  of  Berlin,  we  are  indebted 
largely  for  the  accurate  knowledge  we  now  possess  of  the 
physiology  of  the  eye  and  the  ear.  The  Young-Helmholtz 
theory  of  color  is  still  the  best  interpretation  of  color  sen- 
sations, and  the  studies  in  the  physics  of  harmony  have 
solved  for  us  to  a  very  large  extent  the  problem  of  the  ear. 
When  to  this  is  added  the  measuring  of  the  rate  of  transmis- 
sion of  nervous  impulses  and  the  exposition  of  the  law  of 
the  conservation  of  energy,  it  will  be  seen  how  much  has 
been  added  by  this  scholar. 

The  history  of  special  problems  in  physiology  will  be 
found  noted  in  their  respective  places  in  the  book.  It  is 
hoped  that  the  foregoing  epitome  may  show  the  interested 
reader  the  long  road  by  which  our  familiar  ideas  have 
reached  us.  It  is  believed  that  a  clearer  perception  of  the 
efforts  and  the  struggles  which  it  has  cost  great  men  to 
interpret  for  us  these  phenomena  may  result  in  a  quickened 


HISTORY   OF    PHYSIOLOGY.  21 

appreciation  of  their  labors.  It  finally  justifies  us  in  the 
belief  that  the  future  will  contribute  to  the  science  of  physi- 
ology as  much  as  the  past  has  done,  and  that  many  prob- 
lems which  are  still  almost  wholly  unsolved  may  be  rapidly 
Hearing  their  solution. 


CHAPTER  II. 


THE  CBIvIy  AND  ITS  LIFE. 

Probably  the  most  fundamental  conception  in  biology  is 
that  of  the  cellular  structure  of  all  animals  and  plants.  The 
discovery  that  all  living  things  are  made  up  of  separate  and 
individual  cells  laid  the  scientific  foundation  for  the  sciences 
of  histology  and  embryology,  and  very  materially  modified 
physiological  investigation.  It  is  the  bridge  that  connects 
plants  and  animals,  and  is  the  key  to  the  proper  understand- 
ing of  the  phenomena  of  their  growth  and  development. 
But  such  a  far-reaching  and  clarifying  conception  did  not 
appear  suddenly.  Our  present  notions  are  the  result  of 
much  investigation  and  reach  back  through  the  observations 
of  many  years.  The  ease  and  familiarity  with  which  we 
now  speak  of  cells,  of  protoplasm,  of  nucleus,  etc.,  might 
argue  at  first  sight  that  we  are  dealing  with  a  long  estab- 
lished, always-evident  bit  of  knowledge,  while  as  a  matter 
of  fact  these  ideas  are  even  now  in  the  process  of  formation. 

HISTORICAL  VIEW. 

When  L,eeuwenhoek,  the  pioneer  in  the  use  of  the  micro- 
scope, began  to  extend  human  observations  with  the  aid  of 
this  added  sight  a  new  world  was  opened,  and  with  avidity, 
sometimes  with  mere  curiosity,  observers  subjected  all  sorts 
of  things  to  the  scrutiny  of  the  microscope.  In  this  way 
Robert  Hooke,  of  England,  1667,  while  examining  some- 
what indiscriminately  all  sorts  of  things  with  his  rude  micro- 
scope, placed  a  thin  section  of  ordinary  cork  under  the 
instrument  and  noticed  that  the  section  contained  innumer- 
able little  chambers  which,  because  of  this,  he  called  cells. 
He  had,  of  course,  no  idea  as  to  the  meaning  of  these  cham- 
bers, but  used  the  term  "  cell  "  as  we  still  employ  the  word 
(22) 


THE   CEU,  AND   ITS   LIFE. 


23 


nowadays  when  speaking  of  the  chamber  of  a  prison  as  a 
cell.  Although  Hooke's  notion  regarding  these  chambers 
or  cells  has  long  since  been  changed,  the  term  he  applied 
to  them  has  remained,  and  there  is  little  probability  that  it 
will  ever  be  displaced,  so  firmly  is  it  established  in  biolog- 
ical science. 


Fig.   1.— A    SECTION   OF  WOOD    SHOWING 
THE   CHAMBERED   APPEARANCE. 


Fig.  2.— CELLS  IN  GROWING  WOOD. 


Several  years  later  (in  1671)  Malpighi  and  Grew  each 
published  a  treatise  on  structural  botany  in  which  this 
chambered  or  cellular  appearance  was  noted  as  occurring 
in  many  other  vegetable  tissues  besides  cork.  For  more 
than  a  century  nothing  further  was  done,  and  it  was  not  till 
the  beginning  of  our  own  century  that  the  observations  in 
this  direction  were  renewed.  In  1812  Moldenhauer,  a  Dutch 
scientist,  by  macerating  plant  tissues  succeeded  in  isolating 
individual  cells.  (Experiment  easily  repeated  with  a  ripe, 
mealy  apple.)  This  changed  the  idea  of  Hooke  that  cells 
were  but  empty  chambers  in  a  homogeneous  mass,  to  the 
correct  view  that  cells  are  individual  structures  having  a 
solid  wall  enclosing  the  chamber.  In  this  way  the  cell 
wall  and  not  the  empty  space  seemed  to  be  the  essential 
thing.  Soon  after  this,  however,  Corti  and  Amici  found 
that  many  cells  are  filled  with  a  liquid  sap,  and  in  several 
instances  they  had  observed  this  sap  circulating  in  the  cell 
without  being  affected  by  an  external  power.  Such  further 
observations  emboldened  Meyen,  in  1838,  to  venture  the 
assertion  that  a  part  of  the  cell  sap  must  surely  be  alive. 


24  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

In  the  meantime  Robert  Brown,  1831,  had  discovered  the 
nucleus  inside  the  cell.  Thus  little  by  little  the  contents 
were  considered  as  the  essential  thing  of  the  cell,  rather 
than  the  cell  wall.  To  help  this  view  the  botanist,  Unger, 
in  1843  made  a  series  of  discoveries  of  a  then  astounding 
character.  In  examining  the  green  scum  everywhere  plen- 
tiful on  moist  flower  pots  (vaucheria) ,  he  saw  the  cell  sap 
l<  crawl  "  out  of  the  old  cell  wall  and  creep  away.  This  is 
the  common  phenomenon  of  rejuvenescence  easily  observed, 
in  which  the  protoplasm  leaving  the  old  cell  wall  becomes 
active  for  a  while,  and  then  produces  a  new  vaucheria 
thread.  But  to  Unger  it  was  a  plain  case  of  the  sap  of  a 
plant  cell  turning  into  an  animal.  The  misinterpretation 
was  strengthened  when  soon  afterwards  Kritzing  observed 
green  amoeboid  cells  changing  into  filaments  of  algae.  Here 
was  a  case  of  an  animal  changing  to  a  plant.  But  it  estab- 
lished one  thing  as  correct — that  the  cell  contents  are  the 
essential  thing  and  the  cell  wall  quite  secondary.  To  the 
mysterious  contents  endowed  seemingly  with  vital  proper- 
ties, Hugo  von  Mohl  in  1846  gave  the  name  protoplasm . 

All  these  views  were  then  moulded  into  a  definite  theory 
by  Schleiden  in  1849.  It  will  be  observed  that  up  to  this 
time  all  the  observations  had  been  confined  to  plants,  but 
in  1849  the  histologist,  Schwann,  showed  that  animals,  too, 
are  made  up  of  cells,  and  applied  the  cell  theory  equally  to 
them.  The  theory  was  therefore  called  the  "Schleiden  and 


(__i 


Fig.  3.— CELLS  FROM  THE  ANIMAL  BODY  (CORNEA).     (After  Schafer.) 
c,  columnar  cells;  p,  polygonal  cells;  fl,  flattened  cells. 

Schwann  cell  theory."     The  manner  in  which  these  cells 


THE   CEU,  AND   ITS   LIFE.  25 

originated  was  not  known,  although  the  current  notion  was 
that  new  cells  arose  "  in  between  "  old  cells.  That  a  tiny 
granule,  the  nucleus,  was  in  some  manner  deposited 
between  already  formed  cells,  and  that  around  this  nucleus 
the  rest  of  the  cell  gradually  arose  by  a  process  of  precipi- 
tation like  the  growth  of  a  crystal  in  a  supersaturated  solu- 
tion of  that  substance.  How  inconsistent  that  view  was 
with  all  the  facts  of  heredity  seemed  not  to  be  considered. 
The  remarkable  advance  in  knowledge,  that  a  new  cell 
arises  only  by  a  division  of  a  pre-existing  cell  is  due  to  the 
botanist  Nageli,  who  had  observed  this  manner  of  cell  pro- 
duction. And  when  finally  Max  Schultze  in  our  own  day 
proved  the  identity  of  protoplasm,  whether  taken  from  plant 
or  animal,  the  cell  theory  as  we  now  understand  it,  was  in 
its  general  outlines  established.  Added  proof  was  further 
given  to  this  theory  (now  really  a  fact)  when  Dujardin  and 
Haeckel  showed  that  many  of  the  lowest  animal  and  plant 
forms  were  in  reality  nothing  more  than  single  cells. 

A    TYPICAL   CELL. 

As  the  cell  figures  so  prominently  in  the  proper  under- 
standing of  nearly  all  histological  structures  and  throws  so 
much  light  on  physiological  properties  and  the  problems 
of  heredity,  a  more  general  account  of  it  is  here  given 
as  an  introduction  to  the  histological  matter  further  on.  A 
typical  cell  consists  of  a  mass  of  protoplasm  surrounded  by 
a  cell  wall,  and  containing  within  it  a  nucleus.  Food 
material  also  frequently  occurs  diffused  through  the  pro- 
toplasm. Recently  there  was  discovered  a  further  structure, 
lying  usually  close  to  the  nucleus,  the  centrosome.  The 
exact  nature  of  this  body  is  not  yet  fully  established,  but 
it  seems  to  play  a  very  important  part  in  the  division  of  the 
cell.  The  nucleus  is  made  up  of  a  substance  which  stains 
deeply  when  treated  with  the  usual  staining  agents  and  has 
been  called  chromatin.  The  nucleus  is  that  part  of  the 
cell  which  seems  to  influence  and  determine  the  func- 
tion of  the  cell,  and  from  the  important  role  it  plays  in 


26 


STUDIES   IN  ADVANCED    PHYSIOLOGY. 


Fig.  4 .— AMCEBA.    (After  Leidy.) 
n,  nucleus;    cv,   contractile  vacuole 
(excretory  organ);    N,  food  vacuoles; 
ek,  exoplasm ;  en,  endoplasm. 


Fig.  5.— A  TYPICAL  CELL  FROM  THE  INTES- 
TINAL EPITHELIUM  OF  A  WORM.  (Carnoy.) 
me,  membrane  of  cell ;  pc,  protoplasm  of  the 
cell ;  mn,  membrane  of  nucleus ;  pn,  achroma- 
tin  of  the  nucleus;  bn,  the  chromatin  filament 
about  to  change  into  the  separate  chromo- 
somes. 


the  formation  of  a  new  cell,  is  believed  to  be  the  carrier  of 
those  qualities  and  properties  which  we  are  wont  to  desig- 
nate as  those  of  heredity.  In  cells  which  have  lost  the 
power  of  division  the  nucleus  practically  disappears,  but  it 
is  conspicuous  in  eggs  which  are  about  to  usher  in  a  period 
of  active  cell  division.  By  a  chemical  modification  of  the 
protoplasm  of  the  cell,  the  cell  is  differentiated  into  the  re- 
quired tissue  in  question.  By  changes  of  some  kind  in  the 
protoplasm  of  the  cells  are  brought  about  all  those  phenom- 
ena of  physiology  such  as  secretion,  absorption,  assimilation, 
contraction,  and  some  physiologists  go  on  to  add — conscioiis- 
ness  and  thozight,  a  step  by  no  means  yet  fully  warranted. 

These  various  activities  of  the  cells  will  be  discussed 
in  their  appropriate  chapters,  and  attention  is  called  here 
briefly  only  to  the  somewhat  complicated,  but  interesting 
process  of  the  indirect  division  of  the  cell. 

THE  DIVISION  OF  THE  CELL. 

When  the  process  of  cell  division,  called  karyokinesis,  is 
about  to  be  ushered  in,  the  centrosome  lying  close  to  the 


THE   CEIJ,  AND   ITS   IJFE.  27 

nucleus  is  seen  to  divide,  and  the  two  parts  move  toward 
the  opposite  ends  or  poles  of  the  cell.  Just  what  these 
centrosomes  are  is  still  an  unsettled  question.  Radiating 
from  these  centrosomes  there  soon  appear  little  delicate 
threads,  believed  by  some  observers  to  have  been  derived 
from  the  achromatin  of  the  nucleus;  by  others,  from  the 
protoplasm  of  the  cell  body.  The  threads  between  the 
centrosomes  seem  to  be  continuous,  that  is,  extending 
from  one  centrosome  to  the  other,  and  thus  forming  a  so- 
called  "spindle."  The  continuity  of  these  threads  is 
questioned  by  others,  who  believe  that  they  extend  no 
further  than  the  "  equatorial  plate."  In  the  meantime  the 
nucleus  undergoes  changes  by  which  the  chromatin  of  the 
nucleus  appears  as  a  more  or  less  coiled  thread,  which  soon 
breaks  up  into  a  number  of  V-shaped  loops  called  chromo- 
somes. The  number  of  these  chromosomes  varies  for  the 
different  species  of  animals  or  plants,  but  in  the  same 
species  it  is  practically  constant.  These  chromosomes 
arrange  themselves  in  the  region  of  the  "equatorial  plate." 
A  longitudinal  splitting  of  each  chromosome  doubles  the 
original  number  of  Vs.  Half  of  the  V's  now  move  toward 
the  one  pole,  the  other  half  to  the  opposite  pole. 
Whether  the  spindle  threads  serve  in  any  way  to  draw  or 
guide  the  individual  V's  is  an  interesting  but  unsolved 
question.  When  the  chromosomes  have  arrived  at  their 
destination  the  individual  V's  again  fuse  together,  and  soon 
two  nuclei  have  replaced  the  original  one.  The  cell  proto- 
plasm now  seems  to  arrange  itself  with  reference  to  the  two 
new  nuclei,  and  a  constriction  of  the  old  cell  wall,  or  the 
formation  of  a  new  wall  along  the  line  of  the  equatorial 
plate  finally  produces  two  separate  and  distinct  cells,  which 
in  turn,  by  repeating  this  same  process,  may  produce  two 
more,  etc.  The  extreme  care  in  dividing  the  nucleus 
(which  is  the  bearer  of  heredity)  shows  that  nature  takes 
every  precaution  to  give  to  each  daughter-cell  an  exact 
proportion  of  all  those  attributes  which  heredity  passes 
from  one  generation  of  cells  or  individuals  to  the  next. 


28 


STUDIES   IN   ADVANCED   PHYSIOLOGY. 


Fig.  6.— SHOWING  SOME  OF  THE  STAGES  IN  THE  DIVISION  OF  THE  CELL. 

It  is  interesting  to  observe  that  simple  animals,  who 
in  comparison  with  the  mammals,  say,  have  but  little  that 
is  passed  on  to  the  succeeding  form,  show  a  much  simpler 
type  of  cell  division.  When  we  remember  that  in  the 
chromosomes  of  the  egg  there  are  housed  in  their  finer 
structure  those  determining  influences  which  later  on  will 
reappear  in  the  shape,  size,  structure,  coloration,  intona- 
tion of  voice,  and  even  instincts  of  a  wonderfully  com- 
plicated adult  individual,  we  are  not  surprised  to  see  the 
care  with  which  the  chromosomes  are  elaborated,  for  the 
important  purpose  of  producing  a  new  cell.  While  it 
explains  in  no  sense  the  real  cause  of  heredity,  it  is  appar- 
ent that  in  this  process  there  is  a  valuable  suggestion  as  to 
the  actuality  of  a  physical  basis  for  heredity. 


CHAPTER   III. 


THE    TEACHING  OF   PHYSIOLOGY   AND   THE 
PUBLIC    HEALTH. 

No  one  will  question  the  validity  and  appropriateness  of 
hygienic  considerations  in  a  treatise  on  physiology.  To 
promote  the  individual  and  the  general  health  are  the  pur- 
poses assigned  to  physiology  by  the  law  which  made  it  a 
common  school  subject.  While,  of  course,  there  is  danger 
of  materially  destroying  the  educational  value  of  physiology 
by  having  it  degenerate  into  a  dried  and  cut  code  of  empir- 
ical formulae,  mostly  without  any  real  practical  value;  while 
the  ordinary  school  often  sins  by  spending  valuable  time  in 
giving  platitudinous  advice  which  it  was  never  the  intention 
to  have  followed  to  the  letter,  there  is,  on  the  other  hand, 
the  possibility  of  repaying  a  thousand-fold  the  money  and 
time  expended  in  teaching  physiology  if  there  could  be  put 
into  the  practical  belief  of  all  its  students  a  clear  percep- 
tion of  the  fundamental  laws  that  govern  proper  sanitation 
and  of  the  scientific  methods  of  preventing  disease.  To 
be  obliged  to  acknowledge,  as  true  it  is,  that  most  of  the 
diseases  of  the  human  body  are  due  to  agencies  which  it  is 
entirely  possible  to  control,  and  even  eradicate,  by  properly 
directed  sanitary  and  hygienic  methods,  shows  how  urgent 
is  the  necessity  of  impressing  this  information  upon  the 
attention  of  the  public  at  large. 

In  a  perfectly  healthy  community,  possessed  of  a  per- 
fect system  of  sanitation  and  barring  the  direct  introduction 
of  disease  by  admitting  affected  persons  from  the  outside, 
the  infectious  and  contagious  diseases  would  and  could 
never  appear.  Diphtheria  and  scarlet  fever  would  leave 
children  untouched,  and  consumption  and  typhoid  would 
disappear  from  the  lists  of  mortality.  It  is,  however,  use- 

(29) 


30  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

less  to  effect  sanitary  reforms  by  the  ipse  dixit  of  the 
law.  The  efficiency  of  a  law  is  directly  proportional  to  the 
number  of  people  who  thoroughly  believe  in  its  provisions, 
and  'a  widely  disseminated  knowledge  of  the  conditions  of 
health  and  disease  must  precede  the  statutory  enactment  of 
sanitary  laws.  Our  national  health  must  depend  upon  the 
education  of  the  masses  in  this  direction,  for  repeated  sys- 
tematic attempts  by  some  of  our  cities  to  force  people  into 
cleanliness  and  virtue  by  police  regulations  have  proved 
how  fruitless  such  procedures  are  in  the  end.  The  public 
at  large  is  too  conservative  in  its  modes  of  thinking,  to  fully 
acknowledge  the  value  of  these  proposed  hygienic  reforms, 
for  the  notion  that  nearly  all  disease  is  due  to  a  violation  by 
us  of  some  sanitary  law  is  too  recent  to  be  fairly  established 
in  the  public  mind.  The  wonderful  insight  into  the  nature 
of  contagious  diseases  and  their  prevention  is  almost  wholly 
a  product  of  the  present  decade. 

HISTORY    OF   SANITATION. 

But  it  must  not  be  assumed  that  the  value  of  sanitary 
precautions  was  not  appreciated  at  all  in  former  times,  for 
the  injunctions  and  directions  of  the  Mosaic  code  were  but 
the  attempts  of  the  Jews  to  tabulate  what  experience  had 
proved  to  them  to  be  valuable  in  preserving  their  national 
life.  Their  regulations  with  reference  to  their  food,  and 
their  treatment  of  lepers  clearly  instance  this  point.  The 
observance  of  this  code  is  no  doubt  one  of  the  causes  of  the 
persistence  of  the  Jewish  nation  through  historic  time,  and 
explained  the  comparative  immunity  of  the  Jews  from  the 
epidemics  of  the  Middle  Ages.  The  cruel  and  hard,  but 
terribly  effective  code  of  Lycurgus  for  the  Greeks  had  not 
a  little  to  do  with  the  production  of  the  manhood  of  early 
Greece,  and  the  abandonment  of  this  code  by  the  later 
Greeks  was  one  of  the  elements  that  contributed  to  their 
national  decay. 

The  Romans  also  appreciated  the  value  of  proper  drain- 
age, and  the  Cloaca  Maxima  of  Rome  stands  as  a  monument 


TEACHING   OF    PHYSIOLOGY   AND    PUBLIC    HEALTH.        31 

to  this  day  to  that  effect.  The  remains  of  the  aqueducts 
around  Rome  show  on  what  a  stupendous  scale  the  city  was 
furnished -with  pure  drinking  water.  On  the  other  hand, 
history  plainly  tells  us  that  the  wanton  violation  of  physio- 
logical laws  by  the  pleasure-loving  Romans  of  later  days, 
together  with  the  epidemics  that  repeatedly  devastated  the 
Imperial  city,  had  much  to  do  with  the  decline  and  fall  of 
the  empire. 

It  is,  however,  in  the  Middle  Ages  that  we  see  the  most 
flagrant  violations  of  the  laws  of  health.  The  clothing  of 
the  people  was  made  almost  entirely  of  wool,  and  little 
suited  to  the  varying  temperatures.  The  dwelling  houses 
were  of  the  rudest  construction;  and  clean  floors  were 
unknown.  New  straw  was  placed  from  time  to  time  upon 
the  floors  of  dwellings  to  cover  up  the  filth  that  had  accu- 
mulated there.  A  writer  of  this  period  states  that  when- 
ever he  went  into  a  house  of  this  kind  he  was  immediately 
seized  with  a  fever.  Strong  ale  and  sour  wine,  usually 
drunk  to  excess,  were  prolific  sources  of  disease,  and 
highly  seasoned  and  salted  meats  formed  the  substance  of 
the  daily  diet.  Streets  were  unpaved,  and  almost  to  the 
close  of  the  Middle  Ages  the  man  who  would  have  started 
to  walk  down  the  streets  of  Paris  itself  on  a  rainy  day 
would  have  stepped  into  mud  up  to  his  ankles.  Sewers 
were  unknown,  and  the  filth  and  garbage  were  turned  over 
to  the  slow  process  of  decomposition  in  their  very  midst. 

When  one  remembers  that  there  was  constant  fighting, 
that  people  were  crowded  in  walled  fortresses  and  towns 
without  pure  air,  and  finally  adds  that  the  country  was 
filled  with  murderers,  marauders  and  thieves,  with  frequent 
famines  to  augment  this  class,  one  can  appreciate  what  was 
meant  by  Darwin's  notion  of  the  "  survival  of  the  fittest." 
Only  the  strongest  and  heartiest  survived ;  the  weak  went 
to  the  wall.  It  was  an  illustration  of  Darwin's  law  with 
barbarous  reality.  But  it  gave  to  the  modern  age  a  picked 
race  of  stronger  and  heartier  people.  One  is  not  surprised 
that  under  such  conditions  epidemics  were  plentiful  and 


32  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

famines  frequent.  Thus,  in  the  twelfth  century  there  are 
recorded  fifteen  general  epidemics;  in  the  thirteenth  cen- 
tury, twenty  general  epidemics;  in  the  fourteenth  century, 
eight.  It  was  in  1348  that  Europe  was  devastated  with  the 
epidemic  called  "  The  Black  Death,"  or  "The  Great  Mor- 
tality." In  London,  alone,  100,000  people  were  carried 
away,  and  it  is  estimated  that  on  the  continent  of  Europe 
not  less  than  one-fourth  of  the  population,  that  is,  more 
than  25,000,000  of  people,  fell  prey  to  its  ravages.  The 
imagination  of  to-day  fails  to  picture  the  horror  and  black 
despair  of  the  time.  Throughout  all  this  period  epidemics 
were  believed  to  be  visitations  from  an  angry  God,  and 
there  were  not  missing  observations  of  armies  fighting  in 
the  air,  and  other  supernatural  phenomena  which  served  as 
warnings  and  forerunners  of  these  dread  times. 

With  the  middle  of  the  seventeenth  century  there 
dawned  a  better  day.  Improved  methods  of  agriculture 
and  commerce  materially  bettered  the  daily  food  of  the 
people.  The  introduction  of  tea  and  coffee  replaced  the 
baneful  effects  of  strong  ale  and  spirits;  and  the  intro- 
duction of  the  potato  displaced  the  highly  seasoned  meats. 
Cotton  and  linen  goods  were  revolutionizing  clothing.  But 
possibly  the  greatest  advance  of  all  was  the  discovery  of 
soap.  With  the  introduction  of  this  now  indispensable 
article  the  reign  of  filth  and  uncleanliness  began  to  weaken. 
More  and  more  general  attempts  at  municipal  cleanliness 
resulted,  and  it  began  to  dawn  in  the  minds  of  men  that 
disease  and  filth  had  a  causal  connection.  Men  learned  for 
the  first  time  that  the  prevention  of  disease  might  be  inves- 
tigated as  a  scientific  problem.  Several  remarkable  dis- 
coveries about  this  time  helped  materially  in  the  sanitary 
evolution  of  civilization  at  large.  One  of  these  was  the 
discovery  of  Captain  Cook  that  that  dread  disease,  scurvy, 
might  be  entirely  prevented.  This  disease  had  for  cen- 
turies decimated  the  ranks  of  soldiers  and  sailors,  and  was 
the  especial  dread  of  every  ship's  crew.  The  simple 


TEACHING   OF    PHYSIOLOGY    AND    PUBLIC    HEALTH.        33 

addition  of  lime  juice  to  the  food  of  every  sea-going  vessel 
precluded  the  possibility  of  this  sickness. 

Another  cause  of  great  mortality  was  repeated  out- 
breaks of  jail  fever  in  the  prisons  of  the  country.  This 
disease  was  frequently  carried  from  the  prisons  to  the  outer 
world.  It  was  later  recognized  as  the  typhus  fever  of 
to-day.  It  was  due  to  the  careful  observation  of  John 
Howard  that  this  disease  was  traced  to  filth  and  over- 
crowding. Reforms  based  upon  this  have  made  jails 
healthier  than  many  homes,  and  this  disease  one  of  the 
rarest  occurrence. 

Then,  in  1796,  came  the  discovery  of  Edward  Jenner 
that  smallpox  might  be  prevented  by  the  process  of  vacci- 
nation. While  the  absolute  validity  of  vaccination  is  still 
questioned  by  some  people  to-day,  there  is  no  doubt  about 
the  fact  that  the  mortality  due  to  this  disease  has  been 
many  times  reduced  by  this  process. 

THE  SCIENCE  OF  BACTEEIOLOGY. 

It  was  reserved  to  our  own  day  to  give  us  a  scientific 
insight  into  the  cause  of  disease.  The  science  of  bacteri- 
ology is  a  product  of  the  last  few  years.  At  first  a  small 
branch  of  the  science  of  botany,  bacteriology  has  com- 
manded more  and  more  attention;  has  ramified  in  wider 
and  wider  directions  until  now  it  has  the  dignity  of  a  dis- 
tinct science ;  and  there  are  perhaps  few  subjects  of  study 
which  are  to-day  being  pursued  with  such  an  avidity,  and 
in  which  the  results  obtained  have  proved  of  such  unspeak- 
able worth.  An  elementary  understanding  of  the  more 
important  conceptions  of  bacteriology  is  necessary  to  a 
proper  appreciation  of  hygienic  laws.  No  one  any  longer 
questions  the  cause  of  all  our  contagious  and  infectious 
diseases.  It  is  a  matter  of  every-day  comment  to  speak  of 
the  various  germs  producing  respectively  the  various  con- 
tagious diseases.  A  short  summary  of  the  growth  of  this 
science  may  be  a  matter  of  interest. 


34  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

BACTERIA. 

Very  tiny  living  objects,  visible  only  with  the  higher 
power  of  the  microscope,  had  frequently  been  observed  by 
botanists  and  zoologists.  Their  almost  universal  distribu- 
tion had  been  commented  upon.  Attempts  were  made  to 
properly  classify  them  in  the  system  of  nature.  At  first 
regarded  as  animals,  they  have  finally  been  relegated  to  the 
domain  of  botanists,  and  are  now  viewed  as  belonging  to 
the  plant  kingdom.  But  little  attention  was  paid  to  them 
until  the  remarkable  observation  was  made  that  there 
seemed  to  be  a  causal  connection  between  such  micro- 
organisms and  certain  known  diseases.  It  is  due  to  the 
genius  of  the  Frenchmen  Davaine,  Pasteur  and  Chauveau 
to  have  given  us  the  germ  theory  of  disease,  our  notions  of 
fermentation,  and  the  first  successful  attempts  at  pro- 
tective inoculation,  The  first  disease  that  was  clearly 
proved  to  be  due  to  such  organisms  was  the  splenic  fever, 
which  about  the  middle  of  this  century  was  playing  such 
havoc  with  the  sheep  and  cattle  of  the  continent.  Beyond 
the  peradventure  of  a  doubt  it  was  shown  by  these  French- 
men that  these  little  germs  not  only  caused  the  disease  in 
the  animals  studied,  but  that  such  germs  might  actually  be 
taken  into  the  system  of  other  animals,  and  so  produce  the 
disease  anew. 

A  wonderful  addition  to  our  knowledge  was  made  in 
1872,  when  Klebs  explained  the  phenomena  of  the  inflam- 
mation of  wounds  and  blood  poisoning.  He  had  occasion 
to  examine  numerous  wounded  soldiers  of  the  Franco - 
Prussian  war,  and  observed  that  in  the  wounds  and 
abscesses  of  such  individuals  there  were  always  found  such 
organisms,  and  he  proved  that  even  deeper  portions  of  the 
body  to  which  the  inflammation  had  extended  had  been  so 
diseased  by  the  migration  of  these  micro-organisms  along 
channels  that  he  was  able  to  trace.  Few  discoveries  have 
done  so  much  to  alleviate  human  suffering  and  to  lessen 
the  dangers  of  surgical  operations  as  this  knowledge  that 


TEACHING   OF    PHYSIOLOGY    AND    PUBLIC    HEAI/TH.        35 

inflammation  is  due  to  the  introduction  of  a  foreign  organ- 
ism. And  when  finally  the  celebrated  Lister,  of  Eng- 
land, perfected  his  methods  of  antiseptics  in  surgery,  the 
scientific  basis  was  laid  for  present  surgical  skill.  Only 
three  years  later,  in  1875,  Klebs  succeeded  in  rinding  the 
bacillus  of  diphtheria. 

Then  what  a  contribution  it  was  to  medical  knowledge 
when  the  German  bacteriologist,  Koch,  in  1882,  pub- 
lished his  preliminary  article  in  which  he  proved  that  that 
dread  disease,  consumption,  was  caused  by  such  a  micro- 
organism! Discovery  followed  discovery,  and  in  the  space 
of  but  a  few  years  the  germs  which  cause  cholera,  hydro- 
phobia, lockjaw,  leprosy,  malaria,  typhoid,  and  other  fevers 
were  discovered.  With  this' discovery  it  was  possible  to 
make  experiments  with  a  view  of  preventing  these  diseases. 
It  was  possible  to  work  out  the  life-history  of  the  germ — 
under  what  conditions  it  would  grow  best ;  under  what  con- 
ditions it  would  be  retarded  in  its  growth;  what  agency 
would  suffice  to  destroy  it ;  in  what  manner  it  could  be  car- 
ried from  place  to  place ;  through  what  avenues  it  reached 
the  body.  This  explained  at  once  how  garbage  and  filth 
of  any  kind  were  a  prolific  source  of  disease.  This  explained 
general  epidemics,  but  it  also  suggested  efficient  ways  of 
protection.  The  sterilizing  action  of  heat  was  clear,  and 
the  use  of  antiseptics  was  susceptible  of  everybody's 
understanding.  To  show  what  a  clear  insight  it  gave  into 
diseases  previously  not  at  all  understood,  common  malarial 
fever  may  be  taken  as  an  illustration. 

No  one  could  explain  why  a  patient  should  every  third 
or  fourth  day  be  seized  with  a  fever  paroxysm  and  be  com- 
paratively free  from  the  disease  during  the  intervening  pe- 
riod. No  hint  was  obtainable  anywhere.  What  was  its 
immediate  cause?  Bacteriology  has  revealed  that  this  com- 
mon ailment  is  due  to  a  tiny  organism  (sporozoa)  which 
lives  as  a  parasite  in  the  red  corpuscle  of  human  blood. 
Introduced  into  the  blood  from  various  poorly  drained  areas 
containing  much  decayed  organic  matter,  it  finally  finds 


36  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

lodgment  in  the  corpuscles.  The  corpuscle  containing  this 
parasite  loses  its  vital  properties,  is  robbed  of  its  coloring 
matter,  the  haemoglobin,  and  so  materially  reduces  the 
efficiency  of  the  blood  to  nourish  the  body.  Two  kinds 
of  parasites  have  been  found  which  differ  from  one  another 
in  the  time  required  for  producing  new  spores.  In  one 
species  each  parasite  produces  a  brood  of  new  spores  every 
third  day.  In  the  second  parasite  the  new  brood  arises 
every  fourth  day.  It  is  the  formation  of  this  new  brood  of 
spores  every  third  or  fourth  day  which  causes  the  malarial 
paroxysm,  probably  because  in  the  formation  of  the  spores 
some  poisonous  substance  is  eliminated.  If,  as  it  often 
happens,  the  .patient  houses  in  his  blood  two  sets  of  these 
parasites  whose  times  of  spore  formation  varies,  the  par- 
oxysms vary  accordingly,  and  so  explain  why  the  chill  may 
recur  on  successive  days,  then  miss  a  day  only  to  recur 
again  on  the  fourth  day.  We  understand  how  the  destruc- 
tion of  the  red  corpuscles  of  the  blood  by  these  infesting 
parasites  will  produce  the  anaemia,  so  characteristic  of 
malarial  fever. 

The  germ  of  the  only  too  prevalent  typhoid  fever  we  can 
now  produce  in  pure  .cultures  in  the  laboratory  test  tube. 
We  can  see  how  it  thrives  and  multiplies  in  decaying 
organic  matter.  It  can  easily  be  observed  what  a  healthy 
medium  sewage  water  is,  and  we  can  follow  through  all  its 
vicissitudes  this  agent  of  mortality.  Bacteriology  answers 
satisfactorily  the  prevalence  of  consumption,  the  agent  that 
carries  off  more  victims  than  probably  any  half  dozen  other 
diseases  combined.  Nuttall,  of  Johns  Hopkins  Hospital, 
in  making  quite  a  number  of  careful  calculations  found  that 
a  patient  only  moderately  advanced  in  the  disease  elimi- 
nated from  his  body  in  the  sputum  during  a  short  period  of 
twenty-four  hours,  from  one  and  one-half,  to  four  and  one- 
third  billions  of  bacteria.  These  billions  form  part  of  the 
dust  which  by  the  winds  is  spread  broadcast  and  carries 
infection  to  the  first  susceptible  lung,  or  washed  away  by 
the  rains  finally  finds  its  way  back  through  drinking  water 


TEACHING   OF    PHYSIOLOGY   AND    PUBLIC    HEALTH.        37 

to  some  person,  there  to  set  going  the  various  forms  of 
gastric  or  intestinal  tuberculosis. 

In  such  a  brief  account  we  are  not  specially  concerned 
with  the  question  what  bacteria  are.  Suffice  it  to  say  that 
they  are  minute  organisms,  among  the  smallest  known. 
Several  typical  forms  are  usually  described.  Thus  the  little 
round  globular  form,  such  as  the  germ  that  causes  erysip- 
elas, is  called  micro-cocczis.  The  short  rod-like  form,  such 
as  the  one  that  induces  the  decomposition  of  flesh,  is  called 
bacterium.  (Used  in  this  instance  in  a  special  way  and  not 
referring  to  the  whole  group.)  Longer  rod-like  forms  are 
represented  by  the  germs  of  consumption,  typhoid  fever, 
leprosy,  lockjaw,  etc.,  and  are  called  bacilli.  The  comma 
bacillus  of  Asiatic  cholera  has  a  slightly  bent  shape  not 
unlike  the  comma,  whence  its  name,  and  belongs  to  the 
order  of  the  vibrios.  In  typhus  recurrent  fever  occurs 
the  cork -screw -like  form  called  spiro-chaeta,  while  the 
undulating  snake-like  form  frequently  found  in  the  mouth 
and  the  teeth,  is  called  spirillum.  In  addition  to  the 
active  forms  most  bacteria  are  able  to  produce,  when  the 
necessity  arises,  spores  which  are  able  to  resist  drought  or 
any  other  unfavorable  circumstance  for  a  long  time,  only  to 
germinate  again  as  soon  as  proper  conditions  arise.  The 
resistance  of  some  of  these  spores  is  almost  incredible. 
The  spores  of  the  hay  bacillus,  found  in  ordinary  hay,  may 
be  boiled  several  minutes  without  injuring  their  vitality. 
Spores  may  be  formed  either  by  the  protoplasm  of  a  bac- 
terium forming  a  thick  wall  around  itself  for  extra  protec- 
tion, or  by  the  protoplasmic  contents  of  a  bacillus  splitting 
up  into  several  small  globular  bodies  which  are  soon  pro- 
vided with  a  thick  coat,  and  in  this  form  mingle  with  the 
dust  of  the  atmosphere  to  be  wafted  and  scattered  by  every 
breeze  that  stirs. 

But  it  must  not  be  supposed  that  all  germs  are  disease- 
producing.  Many  of  them  are  of  the  utmost  benefit  to  us. 
The  germs  that  cause  the  ordinary  decomposition  of  organic 
matter  by  returning  it  to  the  elements,  keep  things  clean 


38  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

and  pure,  while  the  bacteria  which  are  found  in  such  great 
numbers  in  the  soil  act  as  a  biological  filter,  destroying  all 
the  impurities  so  that  the  water  at  a  reasonable  depth  is 
entirely  free  from  organic  particles.  The  very  plants  are 
dependent  upon  the  bacteria  of  the  soil  for  their  nitrog- 
enous food.  Botanists  assure  us  that  were  it  not  for  the 
nitrification  caused  by  the  bacteria  in  the  ground  the  entire 
plant  world  would  be  reduced  to  a  stunted  growth.  The 
very  processes  of  digestion  in  the  human  body  are  helped 
along  by  bacteria  which  live  normally  in  the  human  intes- 
tine, and  some  of  the  most  extensive  commercial  enterprises 
are  dependent  upon  fermentations  brought  about  by  the  aid 
of  these  small  organisms. 

HOW  GERMS  PRODUCE  DISEASE. 

The  question  naturally  arises,  just  in  what  manner  these 
bacteria  produce  their  respective  diseases  in  the  body.  Is 
it  due  to  the  depredations  of  the  bacteria  themselves,  or 
some  product  which  they  produce  while  in  the  body?  No 
one  will  question  the  fact  that  much  harm  results  from  the 
actual  destruction  of  tissues  literally  eaten  up  by  these 
germs.  The  gradual  disintegration  of  the  consumptive 
lung  is  more  than  sufficient  evidence,  but  it  is  now  gener- 
ally conceded  that  the  injurious  effects  of  these  bacteria  are 
due  to  poisons  which  they  elaborate  in  the  body  rather 
than  to  their  own  immediate  presence.  These  poisons 
directly  attack  the  tissues,  and  to  their  effect  are  due  the 
symptoms  of  the  disease.  It  has  been  possible  to  extract 
these  poisons  from  animals  afflicted  with  certain  diseases 
and  then  to  inject  this  poison,  free  from  the  bacteria  which 
produced  it,  into  healthy  animals,  there  to  reproduce  all  the 
symptoms  of  the  disease  in  question.  It  is  probable  that 
these  poisons  are  similar  to  the  alkaloids  of  the  organic 
chemist. 

THEORIES  OF  IMMUNITY. 

The  explanation  of  the  fact  that  the  first  attack  of  many 
infectious  diseases  renders  the  person  immune  from  a 


TEACHING    OF    PHYSIOLOGY   AND    PUBLIC    HEALTH.        39 

succeeding  one  is  not  yet  at  hand.  A  number  of  inter- 
esting theories  have  been  advanced  to  account  for  this 
immunity.  Pasteur  held  that  there  was  a  special  food  in 
the  body  which  these  bacteria  needed  and  which  was  com- 
pletely used  up  in  the  first  attack,  thus  making  the  second 
one  impossible;  but  as  the  blood  changes  in  composition 
so  rapidly  it  seems  impossible  that  such  elements  would  not 
again  soon  be  introduced  if  they  were  normally  in  the 
blood.  Then  Chauveau  ventured  the  opinion  that  these 
germs  produce  excretions  which  finally  render  the  blood 
unfit  for  them  to  live  in  and  thus  prevent  the  recurrence  of 
the  disease.  When  we  remember  how  quickly  the  system 
normally  throws  off  foreign  poisons  it  seems  hardly  possible 
that  the  body  should  retain  these  excretions  for  such  a  long 
time  as  the  immunity  seems  to  last.  L,ater,  Grawitz  pro- 
posed the  idea  that  the  outcome  of  a  disease  was  the  out- 
come of  the  battle  waged  between  the  bacteria  in  our  bodies 
and  the  living  tissues,  that  if  the  tissues  managed  to 
obtain  the  upper  hand  and  destroy  the  bacteria  the  training 
so  acquired  would  increase  their  vital  energy  and  resisting 
power  and  so  cut  short  a  second  attack,  something  as  a 
regiment  of  veterans  would  be  less  easily  overcome  in  battle 
than  a  corps  of  raw  recruits.  Succeeding  this  Buchner 
gave  as  his  explanation  that  in  a  first  attack  the  places  at 
which  the  bacteria  were  introduced  became  more  resistant 
and  so  prevented  the  introduction  of  succeeding  ones.  This 
went  on  the  supposition  that  all  kinds  of  bacteria  had  their 
specific  places  through  which  alone  they  could  enter  the 
body.  It  is  not  necessary  to  state  that  this  explanation 
found  little  support. 

Then  came  the  now  celebrated  theory  of  Metchnikoff , 
which  holds  that  the  white  corpuscles  of  the  blood  and 
lymph  are  scavengers  going  up  and  down  between  the  tis- 
sues, and  picking  up  foreign  particles  wherever  found. 
This  picking  up  is  nothing  more  than  the  process  of  amoe- 
boid digestion.  This  theory  is  now  very  generally  accepted, 
and  observations  clearly  show  that  these  corpuscles  do  take 


40  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

into  themselves  under  some  circumstances  foreign  particles. 
Thus  if  a  pus  cell  from  a  wound  be  examined  it  is  usually 
found  to  contain  many  foreign  particles,  usually  bacteria. 
The  corpuscles  with  their  load  of  included  bacteria  are  then 
probably  sent  to  the  spleen  or  liver,  there  disintegrated,  and 
the  injurious  products  eliminated  from  the  body  in  accord- 
ance with  the  regular  physiological  process.  This  theory 
explains  in  a  very  interesting  way  the  phenomena  of  the 
inflammation  of  wounds  and  the  gathering  of  sores.  In  a 
wound  such  as  an  open  cut  the  bacteria  of  the  air  fall  at 
the  first  exposure  and  there  in  the  rich  nutritious  blood 
begin  a  course  of  active  development.  Soon,  however, 
white  corpuscles  congregate  around  the  wound,  the  blood 
usually  following  through  the  openings  in  the  capillaries 
caused  by  their  migrations,  hence  the  redness.  These  cor- 
puscles move  regularly  towards  the  infected  center,  remov- 
ing the  germs  as  they  progress,  until  finally  all  of  the  cor- 
puscles with  their  incepted  germs  meet  in  the  center  of  the 
wound  there  to  be,  possibly  mechanically,  pressed  out  as 
pus.  It  is  known  that  wounds  entirely  protected  from  germ 
contamination  will  not  inflame  at  all,  and  surgical  opera- 
tions of  the  most  violent  character  with  modern  antiseptic 
improvements  may  be  carried  out  without  any  appreciable 
amount  of  inflammation.  Possibly  the  added  vitality  that 
is  supposed  to  come  to  these  amoeboid  cells  in  their  first 
successful  battle  enables  them  to  cut  a  second  venture 
short.  That  these  corpuscles  are  concerned  in  the  elimina- 
tion of  foreign  particles  from  the  blood  is  probably  above 
question,  but  that  this  explains  all  the  phenomena  of 
immunity  is  another  matter. 

The  most  recent  view  and  possibly  the  best  substan- 
tiated one  of  all  is  the  acclimatization  theory,  which  tries 
to  explain  that  we  are  immune  from  a  second  attack  by 
having  become  accustomed  or  acclimated  to  the  poisons  in 
the  first  attack.  To  use  a  not  very  elegant  analogy,  it  is 
like  the  boy  who  can  smoke  his  second  cigar  without  getting 
sick,  because  he  has  been  somewhat  hardened  by  the  first 


TEACHING  OF  PHYSIOIjOGY  AXD  PCBUC  HEALTH,       41 


'.'  -;.:.i::.::  ::  .-  :-r:>.:;  -;;;  > 
to  be  treated  to  a  terrific  dose  of  nicotine  would  be  to  grad- 
ually more  and  more  accustom  himself  to  the  injurious 
:  : 


Just  what  may  be  accomplished  by  gradually  inuring  the 
body  to  poisons  is  remarkable.  By  slowly  increasing  doses, 
sir  -;;.:•.::-.  e  r_:iy  £zilly  be  ^  n;  ::;  .in:  ;:::;:.$  >;  I.i:se  :;::.: 
they  would  have  produced  instant  death  if  administered  for 
the  first  time.  Arsenic  eaters  are  able  to  take  amounts  of 
that  drug  which  would  be  out  of  the  question  by  one  who 
had  never  taken  it  before.  Passably  this  view  explains  the 
philosophy  of  vaccination  and  anti-toxine  methods.  As 
gwfty  one  knows  vaccination  for  smallpox  consists  in  intro- 
duong  a  weakened  form  of  that  virus  into  the  body  which 
there  produces  a  mild  attack  of  smallpox.  In  this  attack 
the  poison  is  developed  so  slowly  and  gradually  that  the 
body  can  adjust  itself  to  these  increasing  amounts  and  a 
succeeding  attack  of  the  violent  form,  would  thus  not  be 
able  to  strike  down  the  energies  of  the  body  at  the  very 
onset  before  possibly  the  body  had  had  time  to  overcome  the 
dangerous  intruder.  In  the  anti-toxine  method  now  used  in 
diphtheria  the  seium  of  a  horse  which  has  had  diphtheria,, 
and  in  which  blood,  therefore,  is  found  some  of  this  diphthe- 
retic  poison,  is  injected  in  small  doses  into  the  body  of  the 
patient  suspected  of  developing  diphtheria.  The  poison  so 
injected  in  small,  or  slightly  increasing  doses  gradually 
allows  the  body  to  adjust  itself  to  it  so  that  later  on  wtien  the 
disease  has  produced  greater  quantities  of  this  same  poison 
the  tissues  have  been  acclimated  to  it  to  such  an  extent  that 
the  poison  does  not  prove  fatal.  As  the  bacteria  them- 
selves can  not  live  when  the  amount  of  the  poison  which 
they  have  formed  becomes  too  great  it  may  be  too,  that  the 
introduction  of  some  of  this  poison  into  a  patient's  blood 
will  serve  to  check  the  growth  of  the  microbes. 

PROBLEMS, 


Hie  specific  germs  of  measles,  yellow  fever,  and  even 

::  .  :    ye:    :.ef.::::e~.y  k:;.  -,-.-_-..  ":  ..:    ::    :::    :;:c 


42  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

success  bacteriologists  have  had  in  studying  other  infectious 
diseases  we  may  reasonably  expect  light  on  these  points  in 
the  not  very  remote  future. 

PRACTICAL   GUIDANCE. 

It  was  not  the  province  of  this  chapter  to  discuss  at  any 
length  bacteriological  problems.  Its  purpose  was  to  call 
attention  to  a  few  scientific  facts  which  should  form  the 
basis  for  a  sensible  appreciation  of  sanitary  and  hygienic 
laws;  and  when  we  remember  that  most  people  die  with 
some  form  of  infectious  or  contagious  disease,  surely  no 
excuse  is  needed  to  press  such  information  upon  the  atten- 
tion of  the  common -school  teacher  who  has  the  greatest 
opportunities  for  distributing  it.  It  is  intended  that  the  few 
points  here  given  shall  lead  to  such  a  general  and  interested 
observance  of  all  rules  and  regulations  to  advance  the  gen- 
eral health,  that  disease  may  become  more  infrequent,  and 
the  length  of  human  life  and  happiness  thereby  materially 
increased.  Possibly  nothing  better  can  be  done  in  this  case 
than  to  quote  here  the  rules  and  regulations  recently  issued 
by  the  Indiana  State  Board  of  Health,  which  are  so  clear  and 
to  the  point  that  they  are  given  without  further  comment: 

Explanation. 


"  Simultaneously  with  the  annual  opening  of  the  public  schools,  diph- 
theria, measles,  mumps,  scarlet  fever  and  many  other  diseases  usually 
increase.  This  is  caused  by  the  congregating  of  the  pupils.  They  mass 
together  and  contact  spreads  infection.  Some  few  pupils  may  have  just 
recovered  from  a  communicable  disease,  or  they  may  be  from  families 
that  have  been  smitten,  and,  being  infected,  they  transmit  disease  to  those 
who  are  susceptible.  It  is  reasonable  to  assume  that  the  suddenly  imposed 
confinement  in  the  schools  after  a  period  of  freedom  frets  the  children  for  a 
few  days,  causing  more  or  less  nervousness  and  so  resistance  is  temporarily 
lowered.  In  this  way  susceptibility  may  be  increased,  and  sickness  may 
more  readily  follow.  To  do  all  that  is  possible  to  prevent  the  usual  school- 
opening  increase  in  illness  is  the  object  of  these  rules. 

"  It  is  ordered  in  the  rules  that  desk  tops  and  banisters  be  washed  with 
soap  and  water  and  afterward  be  treated  with  a  disinfectant.  This  is 
required  because  disease  germs  may  be  planted  upon  exposed  desk  tops  and 
banisters  by  infected  persons,  and,  being  transferred  by  the  children's  hands 


TEACHING    OF    PHYSIOLOGY    AND    PUBLIC    HBAI/TH.        43 

to  their  mouths,  disease  results.     The  washing  and  disinfecting  will  do  much 
to  prevent  infection  from  this  source. 

"  Open  water  buckets  and  large  tin  cups  are  condemned  because  the 
dipping  of  water  with  cups  which  are  used  by  many  introduce  spittle  into  the 
supply ;  and,  besides,  open  buckets  catch  dust  and  dirt.  Diphtheria, 
diarrhoea,  sore  mouth  and  other  complaints  have  been  transmitted  in  this 
way.  This  source  of  disease  may  be  avoided  to  a  considerable  degree  by 
supplying  a  covered  tank  with  a  large  free-flowing  faucet  and  a  small  cup. 
The  opening  of  a  large  faucet  will  furnish  a  strong  stream,  which  will  sud- 
denly fill  the  cup  and  wash  the  saliva  from  the  edge.  Ample  drainage  must 
be  provided  for  carrying  away  the  waste  water. 

"  Slates  are  condemned  because  of  their  uncleanliness.  Writing  and 
figures  being  obliterated  as  they  frequently  are  with  spittle,  and  as  the  damp 
slates  readily  collect  dust,  the  danger  of  the  transmission  of  disease  in  this 
way  is  very  great.  Small  children  generally  place  pencils  and  pens  in  their 
mouths,  and  if  these  articles  are  promiscuously  distributed  without  being 
sterilized,  as  the  rules  direct,  infection  may  result.  The  collecting  of  pencils 
seems  necessary  to  always  insure  one  to  each  pupil. 

"Spitting  is  prohibited  because  it  is  a  possible  source  of  disease,  is 
filthy  and  is  unnecessary. 

*'  It  may  seem  shocking  and  unnecessary  to  many  to  exclude  con- 
sumptives from  the  schools,  but  when  we  stop  to  think  that  tuberculosis 
causes  one  in  every  seven  deaths,  killing  more  people  annually  than  cholera, 
smallpox,  diphtheria,  scarlet  fever  and  yellow  fever  combined,  then  it  is  time 
to  lay  aside  that  sentiment  and  pity  which  would  perpetuate  disease  and 
death,  and  take  on  those  qualities  in  that  higher  form  which  makes  them 
forces  for  more  abundant  and  better  life. 

"  These  rules  may  seem  trifling  and  unnecessary  to  those  who  have  not 
given  consideration  to  modern  sanitation,  but  the  teacher  more  than  any  other 
public  officer  may  secure  the  physical  well-being  of  the  pupils  as  well  as  their 
intellectual  advancement. 

"  It  is  hoped  that  all  the  school  authorities  of  the  State  will  promptly 
enforce  these  rules." 

Special  lliiles. 


RULE  i.  All  teachers  of  public,  private  and  parochial  schools,  all 
county,  city  and  town  health  officers  and  all  school  authorities  shall  refuse 
admittance  to  the  schools  under  their  jurisdiction  of  any  person  from  any 
household  where  contagious  disease  exists,  or  any  person  affected  with  any 
evident  or  apparent  communicable  disease,  or  any  person  who  may  recently 
have  been  affected  with  diphtheria,  membranous  croup,  scarlet  fever,  whoop- 
ing cough,  contagious  skin  disease,  measles  or  other  communicable  disease, 
until  first  presenting  a  certificate  signed  by  a  reputable  physician  stating  that 
danger  of  communicating  such  disease  is  past,  and  said  certificate  is  approved 
and  indorsed  by  the  Health  Officer  in  whose  jurisdiction  the  person  may 
reside. 

RULE  2.  School  Commissioners,  School  Trustees  in  cities  "and  towns, 
nd  Township  Trustees,  and  all  authorities  governing  private  or  parochial 


44  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

schools,  shall  have  the  school  houses  under  their  control  put  in  sanitary  con- 
dition before  school  is  opened  and  kept  so  throughout  the  year.  Floors  shall 
be  scrubbed,  windows  cleaned,  desks  and  all  woodwork  washed  with  soap 
and  water  and  treated  with  a  disinfectant.  Windows  shall  be  in  repair,  so 
that  ventilation  may  be  made  perfect.  Heating  apparatus  shall  be  efficient 
and  in  good  order,  and  dirty  walls  and  banisters  made  clean.  Banisters  and 
tops  of  desks  shall  be  washed  with  soap  and  water  and  treated  with  a  disin- 
fectant once  each  week.* 

RULE  3.  School  Commissioners,  School  Trustees  in  cities  and  towns, 
and  Township  Trustees,  shall  provide  small  drinking  cups  not  to  hold  over  a 
gill.  Buckets  or  pails  to  dip  from  are  condemned,  and  reservoirs  or  tanks  of 
ample  size  having  large,  easy  acting,  free  flowing  faucets  shall  be  provided. 
When  water  is  drawn  direct  from  public  water  pipes  or  pumps,  reservoirs  or 
tanks  are,  of  course,  not  required.  Ample  drainage  facilities  for  waste  water 
shall  be  provided  and  the  pupils  directed  to  allow  the  cups  to  flow  over  when 
the  water  is  drawn.  Drinking  cups  shall  be  cleaned  and  sterilized  daily. 

RULE  4.  Slates  are  condemned.  Paper  tablets  or  pads  shall  be  used 
instead.  Riveted  metal  boxes  of  tin  or  galvanized  iron  with  hinged  covers 
and  of  proper  size,  or  other  approved  apparatus  to  subserve  the  same  purpose, 
shall  be  provided  for  each  school  room.  These  are  to  receive  pens  or  pencils, 
which  must  be  collected  from  the  children  each  day,  and  shall  not  be  again 
distributed  until  box  or  apparatus  with  the  pencils  and  pens  have  been  steril- 
ized by  heating  in  an  oven  at  or  above  boiling  heat  for  one-half  hour. 
School  Commissioners  and  School  Trustees  in  cities  and  towns,  and  Town- 
ship Trustees,  are  directed  to  enforce  this  rule. 

RULE  5.  Heating  and  ventilating  shall  be  looked  after  with  great  care. 
Every  school  room  shall  be  provided  with  a  thermometer  and  a  temperature 
not  exceeding  75°  Fahrenheit,  nor  less  than  65°  be  maintained  during  school 
hours.  School  Commissioners  and  School  Trustees  in  cities  and  towns,  and 
Township  Trustees,  are  directed  to  enforce  this  rule. 

RULE  6.  Janitors  when  sweeping  shall  use  damp  sawdust  or  slightly 
sprinkle,  in  order  to  prevent  dust.  Dusting  shall  be  done  with  damp  cloths. 
School  Commissioners  and  School  Trustees  in  cities  and  towns,  and  Town- 
ship Trustees,  are  directed  to  enforce  this  rule. 

RULE  7.  The  water  supply  shall  be  pure  and  wholesome,  and  closet  or 
privy  facilities  shall  be  unobjectionable.  School  Commissioners  and  School 
Trustees  in  cities  and  towns,  and  Township  Trustees,  are  directed  to  enforce 
this  rule. 


*The  disinfectant  for  treating  desk  tops,  banisters,  etc.,  and  for  use  in  urinals  and 
closets  may  be  cheaply  made  by  the  following  formula  and  kept  on  hand  in  any  quantity 
desired.  To  make  ten  gallons:  Chlorinated  lime.  40  ounces;  soft  water,  ten  gallons. 
Thoroughly  stir  together  and  let  stand  until  clear.  The  undissolved  lime  will  fall  to  the 
bottom  and  the  clear  supernatant  liquid  may  be  used  on  the  desks,  banisters,  base 
boards,  etc.  The  fresh  milky  mixture,  as  well  as  the  creamy  sediment,  may  be  used  in 
urinals,  closets  and  sinks.  This  disinfectant  is  not  poisonous  or  dangerous.  Chloride  of 
lime  of  the  best  quality  may  be  purchased  in  quantity  for  5  cents  per  pound.  The  cost  of 
the  disinfectant  is,  therefore,  less  than  2  cents  per  gallon.  The  use  of  all  patent  or  secret 
disinfectants  is  discouraged  by  the  State  Board  of  Health. 


TEACHING    OF    PHYSIOLOGY   AND    PUBLIC    HEALTH.        45 

RULES.  Spitting  on  the  floor  of  any  school  building  is  absolutely  for- 
bidden. Teachers  and  all  school  authorities  are  directed  to  enforce  this  rule. 

RULE  9.  School  Commissioners  and  School  Trustees  in  cities  and 
towns,  and  Township  Trustees,  shall  not  employ  teachers  who  are  afflicted 
with  pulmonary  tuberculosis  or  any  constitutional  contagious  disease ;  neither 
shall  they  permit  pupils  so  affected  to  attend  school ;  nor  shall  they  permit 
filthy  or  unclean  pupils  to  attend  the  schools  under  their  control. 


CHAPTER  IV. 
GENERAL  DEFINITIONS. 

PHYSIOLOGY. 

Physiology  is  that  science  which  seeks  to  discover  and 
interpret  those  phenomena  of  plants  and  animals  which  we 
are  wont  to  designate  as  vital.  Man  himself  belongs  to  the 
animal  world,  and  his  physiology  is  to  be  the  subject  of 
this  book.  But  as  most  of  our  knowledge  of  human  phy- 
siology is  derived  from  experiments  on  the  lower  animals, 
it  would  be  nearer  the  exact  state  of  things  to  call  this 
treatise  "Studies  in  Advanced  Animal  Physiology. ' '  But  the 
processes  and  phenomena  of  life  are  universal,  and  the 
division  into  even  plant  and  animal  physiology  is  arbitrary 
rather  than  natural.  There  is  but  one  physiology,  because 
there  is  but  one  life,  although  it  may  be  illustrated  in  vary- 
ing aspects  in  different  groups  of  beings.  The  plant  phys- 
iologist as  well  as  the  animal  physiologist  is  addressing 
himself  to  the  solution  of  the  same  problem:  What  is  life, 
and  what  are  its  phenomena  ? 

Physiology  did  not  become  a  science  in  the  real  sense 
of  the  word  until  it  was  discovered  that  physiological  pro- 
cesses were  based  upon  the  general  laws  of  nature,  and  that 
vital  phenomena  were  never  in  conflict  with  inorganic 
laws.  It  was  not  until  even  recent  years,  almost  in  our 
own  decade,  that  the  old  notion  of  a  vital  energy  was 
finally  abandoned.  Formerly  a  phenomenon  of  life  was  con- 
sidered sufficiently  explained  when  it  was  said  that  it  was 
the  product  of  a  mysterious  vital  energy,  whose  workings 
need  not  at  all  be  in  conformity  with  the  established  laws  of 
nature,  and  which,  consequently,  could  not  form  a  proper 
subject  for  scientific  inquiry.  But  the  idea  of  this  vital 
energy  is  gone  forever,  and  the  fundamental  maxim  of  to- 
'  (46) 


GENERA^   DEFINITIONS.  47 

day  is  that  all  physiological  phenomena  (excepting  those  of 
consciousness,  possibly)  may  be  explained  in  terms  of 
chemistry  and  physics.  Thus,  what  uses  organs  and  tissues 
have,  becomes  a  physical  and  chemical  question  in  essence 
rather  than  a  biological  one. 

ANATOMY. 

Before,  however,  vital  phenomena  can  be  studied,  it  is 
necessary  that  we  should  know  the  structure  of  the  body 
exhibiting  these  phenomena;  and  so  physiology  must 
always  be  logically  preceded  by  the  study  of  anatomy.  As 
these  phenomena  usually  exhibit  themselves  in  the  ultimate 
biological  structure  of  tissues  and  organs,  anatomy  must  be 
extended  with  the  aid  of  a  microscope  to  the  minute  struc- 
ture of  every  part.  The  study  of  this  minute  structure  is 
designated  as  histology. 

COMPARATIVE  ANATOMY. 

After  the  structure  of  the  body  in  question  is  known, 
and  the  function  of  the  various  parts  established,  and  pos- 
sibly even  some  notion  gained  as  to  the  care  that  ought  to 
be  exercised  in  properly  preserving  it,  that  is,  its  hygiene 
understood,  our  knowledge  is  still  very  inadequate.  We 
must  compare  the  form  in  question  with  other  animal  forms, 
for  the  most  helpful  knowledge  of  anything  is  frequently 
that  which  deals  with  the  relations  of  that  thing  to  others. 
Thus,  the  study  of  comparative  anatomy  helps  to  materi- 
ally clarify  the  individual  anatomy  in  question. 

EMBRYOLOGY. 

« 

But  even  this  information  is  inadequate.  Even  when 
we  have  made  extended  comparisons  with  the  related  forms 
much  is  still  left  unsolved  until  we  know  how  this  individual 
structure  came  to  be.  The  science  which  seeks  the 
sequence  of  changes  which  finally  leads  to  the  adult  form 
from  its  primitive  beginning  in  the  egg,  is  the  science  of 
embryology. 


48  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

CLASSIFICATION. 

When  all  of  these  data  concerning  any  living  thing  are 
known  we  have  the  information  at  hand  to  properly  classify 
it  in  the  grand  system  of  nature,  and  to  determine  in  what 
group  or  family  it  finds  its  natural  place. 

A  mere  glance  at  the  human  body  reveals  a  multiplicity 
of  structures,  all,  however,  co-ordinated  to  one  general  pur- 
pose. Thus,  we  have  the  system  of  the  supporting  tissues, 
which  preserve  the  form  and  sustain  the  weight  of  the 
body ;  a  complicated  system  of  muscles  used  in  performing 
our  movements ;  a  generally  distributed  nervous  system  to 
exercise  a  controlling  influence,  and  so  on  through  the  many 
instances  which  might  be  here  adduced.  For  arbitrary 
rather  than  natural  reasons  the  discussion  of  human  physi- 
ology is  here  divided  into  the  following  chapters,  each  of 
which  seeks  to  treat  in  detail  of  some  particular  system  of 
the  body. 


CHAPTER  V. 


THE  BLOOD. 

GENERAL  POINTS. 

When  an  incision  is  made  into  a  living  body  there  at 
once  streams  out  a  reddish-looking  liquid  familiar  to  every 
one  as  blood.  If  this  substance,  which  seems  at  first  sight 
nothing  but  a  liquid,  is  examined  under  a  lens,  it  is  found 
that  the  liquid  itself  is  not  red,  but  that  its  color  is  due  to 
little  particles  which  are  colored  red,  suspended  in  it."  These 
little  particles  are  the  red  corpuscles  of  the  blood,  whose 
coloring  is  due  to  an  iron  compound  called  haemoglobin. 
So  accustomed  have  we  become  to  the  association  of  red- 
ness with  blood  that  one  feels  tempted  at  first  view  to  deny 
the  existence  of  blood  to  those  forms  whose  circulating 
liquid  is  not  colored  red.  But  the  blood  of  most  of  the 
invertebrates  is  colorless  and  devoid  of  this  pigment. 

The  necessity  for  blood  is  too  evident  to  need  comment. 
Tissues  in  various  parts  of  the  body  must  have  nourish- 
ment brought  to  them  and  must  have  their  wastes  removed, 
and  these  results  can  be  obtained  only  by  having  a  circu- 
lating medium  which  shall  answer  to  this  purpose.  Some 
of  the  few-celled  animals  so  small  that  the  juices  may 
reach  all  parts  of  their  bodies  by  the  mere  process  of 
osmosis,  possess  no  real  blood  at  all.  Most  of  the  lower 
forms  are,  however,  provided  with  a  circulating  fluid  quite 
similar  to  the  blood  of  the  vertebrates,  except  that  it  con- 
tains no  red  corpuscles.  The  colorless  blood  of  the  clam 
and  oyster  are  matters  of  common  observation.  In  some 
of  these  invertebrates  the  liquid  itself  is  colored  red  with 
haemoglobin,  as  for  instance,  in  the  earth  worm,  whose 
reddish  blood  vessels  are  easily  seen  through  the  transpar- 
ent skin,  while  in  certain  exceptional  forms  actual  colored 
4  (49) 


50  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

elements  containing  haemoglobin,  no  doubt  identical  with 
blood  corpuscles,  do  really  occur.  It  is  a  matter  of  interest 
that  coloring  matters  other  than  haemoglobin  occur.  Thus 
in  the  cuttlefish,  some  snails,  and  the  lobster,  a  bluish  com- 
pound containing  traces  of  copper,  called  hsemocyanin, 
colors  the  blood. 

The  white  corpuscles  are  distributed  throughout  the  blood 
of  the  invertebrate  world.  When  we  come  to  the  verte- 
brated  or  back-boned  animals,  there  are  in  addition  to  these 
white  corpuscles,  the  red  ones.  The  lowest  vertebrate 
animal  (amphioxus),  however,  possesses  no  red  corpuscles. 

AMOUNT.  * 

The  amount  of  blood  in  the  human  body  has  been  esti- 
mated by  a  number  of  observers  to  be  about  one-thirteenth 
of  the  weight  of  the  body,  thus  making  for  the  average 
person  from  twelve  to  fifteen  pounds  of  blood,  and  calcu- 
lating a  pound  of  blood  to  measure  about  a  pint,  would 
give  us  in  the  neighborhood  of  one  and  one-half  gallons  of 
this  fluid.  This  amount  of  blood  is  at  any  one  time  dis- 
tributed as  follows:  One-fourth  of  it  is  in  the  heart  and 
the  neighboring  large  blood  vessels,  one-fourth  of  it  is 
found  in  the  liver,  one-fourth  in  the  capillaries  of  the  vol- 
untary muscles,  the  remaining  one-fourth  being  distributed 
over  the  rest  of  the.  body.  If  fresh  blood  drawn  from  the 
veins  or  arteries  of  an  animal  be  allowed  to  run  into  a 
vessel  and  there  prevented  from  clotting,  in  a  way  to  be 
noted  later,  the  suspended  particles  or  corpuscles  being  a 
little  heavier  than  the  liquid,  sink  to  the  bottom  and  occupy 
about  fifty  per  cent,  of  the  volume  in  their  wet  condition. 
Examination  of  these  solid  particles  of  the  blood  reveals 
two  kinds  of  corpuscles — one  the  red  corpuscle  already 
mentioned,  the  other  the  colorless  corpuscle,  sometimes 
called  lymph  corpuscle  or  leucocyte.  The  existence  of  a 
third  corpuscle,  that  of  the  placques  or  blood  tablets,  as 
a  distinct  structure,  is  questioned  by  some  physiologists, 
and  a  further  discussion  of  this  element  of  the  blood  is 


THK    BLOOD. 


51 


Fig.  7.— HUMAN  BLOOD.  MAGNIFIED  ABOUT  1000  DIAMETERS.  (After  Schafer.) 
r,  r,  single  red  corpuscles  seen  lying  flat;  r',  r' ,  red  corpuscles  on  their  edge  and 
viewed  in  profile;  r",  red  corpuscles  arranged  in  rouleaux;  c,  c,  crenate  red  corpuscles; 
p,  a  finely  granular  pale  corpuscle;  g,  a  coarsely  granular  pale  corpuscle.  Both  have  two 
or  three  distinct  vacuoles,  and  were  undergoing  changes  of  shape  at  the  moment  of  ob- 
servation; in  g,  a  nucleus  also  is  visible. 

included    in  the  explanation    of    the  phenomena  of    coag- 
ulation. 

THE  RED  COEPUSCLES  OF  THE  BLOOD. 

1. —  Their  Size  and  Form.  The  red  corpuscles  of  human 
blood  are  biconcave,  circular  disks  having  a  diameter  of 
•g-Toif  inch.  They  have  no  definite  membrane  and  are  with- 
out a  nucleus.  In  fresh  blood  these  corpuscles  show  a 
tendency  to  run  together  in  rows  called  rouleaux,  the 
reason  for  which  is  not  definitely  known.  The  peculiar 
reflection  of  the  light  through  the  concave  center  gives  to 
them  when  viewed  with  a  microscope  the  appearance  of 
having  a  nucleus.  It  is,  however,  a  mere  optical  illusion. 
The  size  of  these  corpuscles  as  a  rule  increases  as  we  go 
down  the  animal  scale.  The  largest  corpuscles  are  found 
in  the  salamander-like  proteus,  in  which  they  can  be  actu- 
ally individually  seen  by  the  unaided  eye.  In  Figure  8 
there  are  indicated  drawn  to  the  same  scale,  the  relative 
sizes  and  forms  of  red  corpuscles  of  several  different  ani- 


52 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


Fig.  8. — RED  BLOOD  CORPUSCLES.     (After  Frey.) 

1,  human;  2,  camel;  3,  pigeon;  4,  proteus;  5,  salamander;  6,  frog;  7,  snake;  8,  lani- 
prey.     (a,  surface  view;  l>,  side  view.)     (Drawn  on  same  scale.) 

mals.  With  the  exception  of  the  camel,  whose  corpuscles 
are  slightly  oval,  all  the  corpuscles  of  the  mammals  are 
round.  They  are  further  easily  distinguished  from  those  of 
the  lower  animals,  as  in  the  latter  the  red  corpuscles 
possess  a  distinct  nucleus.  It  is  interesting  that  in  the  em- 
bryonic state  of  the  human  being  nucleated  corpuscles 
occur. 

2. — Color.  When  seen  singly  the  corpuscles  do  not 
appear  red  but  have  a  yellowish  tint,  sometimes  shading 
over  into  a  greenish.  This  is  due,  of  course,  to  the  dilution 
of  the  coloring  matter  when  a  single  corpuscle  is  looked  at. 
But  the  color  of  ordinary  blood  is  not  alone  due  to  the 
actual  color  of  the  haemoglobin,  but  also  to  the  reflection  of 
the  light  from  the  innumerable  little  concave  mirror-like 
surfaces  of  these  corpuscles.  This  explains  why  blood 
becomes  "laky"  in  color  when  the  coloring  matter  is 
extracted  from  the  corpuscles  and  dissolved  in  the  liquid. 
Such  laky  blood  becomes  transparent  and  dark  in  color.  If, 
on  the  other  hand,  certain  mineral  salts  be  added  to  the 
blood  which  cause  the  corpuscle  to  shrink,  the  blood 


THE  BLOOD.  53 

becomes  much  brighter  in  color,  because  owing  to  .the 
shrinkage  of  these  corpuscles,  the  light  which  is  reflected 
from  them  is  correspondingly  concentrated. 

3. — Number.  Careful  and  repeated  counts  of  the  num- 
ber of  red  corpuscles  contained  in  human  blood  have  been 
made  showing  that  in  a  cubic  millimeter  of  blood  (small 
drop)  there  are  in  males  about  five  millions,  and  in  females 
about  four  and  one-half  millions.  This  number  varies  a 
little;  it  is  decreased  after  a  hearty  meal,  after  severe  hem- 
orrhages, after  prolonged  fasting,  or  in  such  sickness  as 
leukaemia,  in  which  the  decrease  in  number  explains  the 
general  paleness  of  complexion.  The  number  to  the  cubic 
millimeter  varies,  however,  greatly  in  different  animals.  In 
the  form  proteus  with  its  huge  corpuscles,  there  are  thirty- 
six  thousand ;  in  the  frog  four  hundred  thousand ;  in  birds 
three  million  six  hundred  thousand,  while  in  the  llama,  of 
South  America,  it  reaches  the  enormous  number  of  fourteen 
millions.  Compared  with  the  white  corpuscles,  in  human 
blood  there  are  from  four  to  five  hundred  red  to  one  white. 

4. — Surface.  In  spite  of  their  small  size  such  large 
numbers  give  a  combined  surface  which  is  surprisingly 
large.  Taking  the  amount  of  blood  in  the  average  body  as 
about  six  pints,  the  total  surface  of  all  the  contained  cor- 
puscles would  not  be  far  from  four  thousand  square  yards. 
This  would  be  a  surface  that  would  require  more  than 
eighty  steps  to  walk  across  it  at  its  shortest  distance.  It  is 
a  surface  over  twenty-five  hundred  times  greater  than  the 
entire  surface  of  the  body.  As  about  one  hundred  and  sev- 
enty-six cubic  centimetres  of  blood  pass  into  the  lungs  in 
each  second  of  time,  it  means  that  a  corpuscle  surface  of 
not  much  less  than  one  hundred  square  yards  is  exposed  to 
the  action  of  the  oxygen  in  this  short  space  of  time.  Does 
this  not  help  one  to  understand  the  rapidity  with  which  the 
oxygen  is  taken  up  and  distributed  as  well  as  the  amount 
carried? 

5. — Composition.  The  essential  element  of  the  red  blood 
corpuscle  is  the  red  haemoglobin  imbedded,  so  to  speak,  in 


54  ADVANCED   STUDIES    IN    PHYSIOLOGY. 

the.  frame  work  or  body  of  the  corpuscle,  which  latter  is 
called  the  stroma.  As  haemoglobin  is  soluble  in  many 
liquids  it  can  easily  be  dissolved  out  of  the  corpuscle  and 
the  colorless  body,  or  stroma  left.  Haemoglobin  possesses 
in  a  remarkable  way  the  ability  to  unite  with  oxygen  when 
that  gas  is  plentiful,  and  to  give  it  up  again  when  the  gas 
is  not  plentiful.  It  is  this  property  which  gives  to  it  its 
important  function  in  the  body.  A  large  amount  of  oxygen 
is  required  in  the  body  to  keep  up  the  relatively  high  and 
constant  temperature,  and  to  make  possible  the  large 
expenditures  of  energy  which  are  necessary  to  maintain 
life.  The  mere  liquid  plasma  of  the  blood  would  be  per- 
fectly unable  to  carry  this  oxygen  in  sufficient  amounts. 
While  this  plasma,  like  water,  which  is  its  main  constit- 
uent, can  dissolve  a  little  oxygen  —  we  know  that  fishes 
derive  their  oxygen  out  of  the  water  in  which  it  is  dissolved 
—  our  own  experience  shows  us  how  limited  this  supply  is, 
and  how  constantly  water  must  be  renewed  in  aquaria  to 
make  possible  the  existence  of  life  in  it.  It  is  estimated 
that  the  haemoglobin  carries  about  nine-tenths  of  all  the 
oxygen.  It  is  not  necessary  to  call  attention  to  the  result 
that  would  follow  doing  away  with  this  haemoglobin  and  so 
reducing  the  oxygen  supply  ninety  per  cent. 

The  Oxygen -carry  ing  Property  of  HcemogloUn. 

The  at  first  puzzling  question,  why  the  haemoglobin 
should  unite  with  the  oxygen  in  the  lungs  and  then  give  it 
up  in  the  tissues  and  not  attempt  at  times  to  carry  the  oxy  • 
gen  from  the  tissues  to  the  lungs,  is  easily  explained  on 
physical  and  chemical  grounds.  Haemoglobin  will  combine 
with  the  oxygen  when  it  is  exposed  to  an  atmosphere  that 
has  a  pressure  of  at  least  one-sixth  of  the  normal  atmos- 
pheric pressure.  Exposed  to  an  atmosphere  less  than  one- 
sixth  of  the  normal  pressure  it  not  only  refuses  to  unite 
with  oxygen,  but  actually  disunites  with  the  oxygen  which 
it  already  has  and  sets  it  free.  Now  we  know  that  the 
atmosphere  is  composed  of  about  four-fifths  of  nitrogen  and 


THE   BLOOD.  55 

one-fifth  of  oxygen,  and  as  the  combined  pressure  of  these 
two  gases  is,  generally  speaking,  fifteen  pounds  to  the 
square  inch,  it  is  evident  that  the  oxygen  part  of  that  pres- 
sure is  one-fifth  of  that,  or  three  pounds,  while  in  an  atmos- 
phere diminished  to  one-sixth  of  fifteen  pounds,  or  two  and 
one-half  pounds,  the  oxygen  part  of  this  would  be  one-sixth 
of  three  pounds,  or  one-half  pound. 

To  state  it  again,  haemoglobin  will  unite  with  oxygen 
when  it  is  exposed  to  an  oxygen  pressure  of  one-half  pound 
or  more,  and  will  not  only  refuse  to  unite,  but  actually  dis- 
unite when  it  is  exposed  to  an  oxygen  pressure  less  than 
one-half  pound.  As  the  oxygen  pressure  in  the  lung  is 
three  pounds,  it  explains  the  union  with  that  gas  there, 
while  the  fact  that  it  gives  up  its  oxygen  in  the  tissues  is 
accounted  for  by  the  simple  physical  reason  that  the  oxygen 
pressure  in  the  tissues  is  less  than  one-half  pound,  as  the 
oxygen  there  is  being  continually  used  up  by  the  hungry 
tissues.  Why  this  haemoglobin  should  be  "  boxed  up  "  in 
corpuscles  and  not  simply  dissolved  in  the  plasma  of  the 
blood,  is  evident.  It  could  carry  as  much  oxygen  in  one 
case  as  in  the  other;  but  as  much  of  the  plasma  soaks 
through  the  capillaries,  becomes  lymph,  bathes  the  tissues, 
and  only  after  a  considerable  time  is  finally  poured  back 
into  the  blood  stream,  it  means  that  any  haemoglobin  dis- 
solved in  this  would  have  been  able  to  carry  but  one  load, 
instead  of  a  hundred,  possibly,  by  being  whirled  along  with 
the  blood  stream. 

When  combined  with  oxygen  (then  called  oxyhaemo- 
globin)  it  is  of  a  bright  red  color,  the  color  of  arterial  blood. 
Haemoglobin  is  an  albuminous  compound  characterized  by 
a  relatively  large  amount  of  iron,  although  in  actual  quan- 
tity the  iron  contained  is  less  than  one-half  of  one  per  cent. 
This  iron,  however,  plays  a  very  important  role  in  the 
oxygen-carrying  process.  The  rapidity  with  which  ordi 
nary  iron  unites  with  oxygen,  or  as  we  say,  "  rusts,"  may 
account  for  its  presence  here. 


56  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

Blood   Crystals. 

As  before  stated,  haemoglobin  can  be  dissolved  out  of 
a  corpuscle  by  adding  to  the  blood  an  excess  of  water, 
chloroform,  or  other  solvent.  If  to  such  a  solution,  made 
icy  cold,  some  alcohol  be  added,  the  haemoglobin  will 
separate,  and  fall  to  the  bottom  as  well-defined  red  crystals 
called  blood  or  haemoglobin  crystals.  It  is  exceedingly 


*     «.  .  - 

—         *'  - 

Fig.  9.— HEMOGLOBIN  CRYSTALS. 
1,  a  typical  crystal.  Fig.  10.— HEMIN  CRYSTALS. 

difficult   to   preserve    these    crystals,    as    they  disintegrate 
easily. 

Under  ordinary  circumstances  haemoglobin  disintegrates  ' 
into  an  albumen  called  globulin,  and  into  a  dirty  brown 
substance  called  haematin.  Hence  the  dirty  brown  red 
appearance  of  old  stains  and  the  discoloration  of  the  skin 
which  follows  a  severe  bruise  and  is  familiar  to  every  boy 
as  a  "  black  eye."  The  discoloration  of  the  skin  is  due  to 
the  blood  which  has  stagnated  in  the  bruised  tissues,  the 
haemoglobin  of  which  has  disintegrated  into  a  substance 
almost  identical  with  haematin  called  haematoidin. 

Sometimes  it  becomes  desirable  to  establish  the  identity 
of  stains  believed  to  be  blood  stains.  It  is  not  at  all  un- 
usual in  legal  proceedings  incident  to  murder  trials,  to 
attempt  to  prove  that  certain  spots  or  stains  are  really 
blood  stains.  Such  a  proof  is  easily  made.  If  from  the 
old  blood  stain  some  of  this  dark  haematin  be  removed  to  a 


THE   BLOOD. 


57 


glass  slip,  a  crystal  of  common  salt  added,  and  a  drop  of 
glacial  acetic  acid  poured  over  it,  the  hsematin  will  unite 
with  some  hydro-chloric  acid  liberated,  and  form  character- 
istic crystals  called  haemin  crystals. 

The  Spectrum  of  Hemoglobin. 

Another  characteristic  property  of  haemoglobin  is  its 
absorption  lines  when  viewed  with  a  spectroscope.  When 
ordinary  white  light  is  viewed  with  a  spectroscope  it  is 
broken  up  into  those  characteristic  colors  with  which  we 
are  familiar  as  the  spectrum.  If,  now,  such  a  beam  of 
ordinary  light  be  passed  through  a  solution  of  oxyhsemo- 
globin  before  reaching  the  spectroscope,  the  spectrum  is  not 
complete;  but  there  appear  two  very  dark  black  lines  in 
that  part  of  the  spectrum  where  the  red  shades  over  into 
the  yellow  and  that  into  the  green.  If  now  the  oxygen  be 
taken  out  of  the  oxyhsemoglobin  and  a  ray  of  light  passed 
through  this  venous  haemoglobin  be  examined,  there 
appears  in  the  spectrum  one  dark  band,  in  position  almost 
exactly  between  the  two  stripes  of  the  oxyhsemoglobin. 
This  single  absorption  band  for  the  haemoglobin,  and  the 
two  bands  for  the  oxyhaemoglobin  are  so  characteristic  that 


Oxyhaemogflobin. 


CO-  haemoglobin. 


Fig.  11.— SPECTRUM  OF  HEMOGLOBIN  AND  ITS  COMPOUNDS.     (C,  D,  E,  etc.,  Fraunhofer 
lines.) 


58  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  presence  of  very  small  amounts  of  blood  in  any  solution 
can  be  established  beyond  a  donbt. 

Haemoglobin  shows  a  strong  affinity  for  carbon  monox- 
ide, the  poisonous  substance  which  forms  a  large  part  of 
ordinary  illuminating  gas.  This  affinity  is  in  fact  so  strong 
that  when  the  haemoglobin  has  once  united  with  the  car- 
bon monoxide  it  is  almost  impossible  to  displace  it.  This 
fact  renders  gas  poisoning  extremely  dangerous,  for  even 
when  such  a  patient  is  brought  into  the  fresh  air,  he  is 
unable  to  get  oxygen,  because  the  haemoglobin  will  not  let 
go  of  its  carbon  monoxide,  and  so  he  is  liable  to  suffocate 
even  in  an  oxygen  atmosphere.  Haemoglobin  so  united 
with  carbon  monoxide  has  a  bright  arterial  appearance, 
and  persons  who  have  died  of  gas  suffocation  maintain  the 
bright  arterial  color  even  long  after  death.  Such  a  corpse 
retains  a  redness  of  skin  which  makes  it  at  first  sight  seem 
almost  impossible  that  the  individual  should  be  dead.  As 
accidents  of  gas  poisoning  are  not  at  all  infrequent  in 
cities,  it  is  worth  while  to  know  how  to  establish  such  a 
cause  of  death. 

In  addition  to  the  haemoglobin,  which  amounts  in  a 
dried  corpuscle  to  over,  ninety  per  cent.,  there  is  an  albu- 
men called  globulin,  further  traces  of  fat,  and  of  two  organic 
substances,  cholesterin  and  lecithin  (to  be  studied  further  in 
later  chapters),  and  finally  salts  of  potassium,  phosphates, 
and  traces  of  ordinary  common  salt.  In  the  live  condition 
of  the  corpuscle  a  large  quantity  of  water  enters  into  its 
constitution. 

6. — Consistency.  In  consistency  the  red  corpuscle  seems 
to  be  made  up  of  a  homogeneous,  jelly-like  substance 
which  possesses  remarkable  powers  of  elasticity.  In  exam- 
ining the  blood  streaming  through  the  blood  vessels  one 
may  find  here  and  there  a  corpuscle  caught  where  an  artery 
divides,  very  much  stretched  out  of  its  natural  shape,  yet 
springing  back  to  its  original  form  as  soon  as  the  stress  is 
over.  This  is  no  doubt  a  valuable  property  in  enabling  the 


THE    BLOOD. 


59 


corpuscles  to  elbow  their  way  through  the  delicate  capil- 
lary channels. 

7.  —  The  Origin  of  the  Red  Corpuscles.  One  of  the 
most  difficult  chapters  in  physiology  is  that  dealing  with 
the  origin  of  the  red  corpuscles,  and  a  number  of  conflict- 
ing theories  are  even  now  seeking  support.  To  trace  the 
origin  of  the  red  corpuscles  it  is  necessary  to  study  the 
blood  of  an  animal  before  its  birth.  Such  examination  of 
human  embryos  shows  that  in  early  uterine  life  the  red  cor- 
puscles are  nucleated  and  possess  the  power  of  amoeboid 
movement.  They  are,  in  fact,  very  similar  to  the  white 
corpuscles  of  the  blood  except  that  they  are  colored  with 
haemoglobin.  These  corpuscles  arise  in  this  way: 

Some  of  the  connective  tissue  cells  become  somewhat 
elongated  and  have  their  nuclei  divide  up  into  many 


Fig.  12.— EMBRYONIC    DEVELOPMENT   OP   BLOOD    CORPUSCLES   IN   CONNECTIVE    TISSUE 

CELLS,  AND  THE  TRANSFORMATION  OF  THE  LATTER   INTO   BLOOD  CAPILLARIES.       (After 

Schafer.) 

«,  an  elongated  cell  with  fluid  protoplasm  and  containing  corpuscles  which  are  still 
round;  6,  a  more  hollowed  cell  in  which  the  corpuscles  have  become  disc-shaped;  c,  the 
manner  of  union  of  such  a  tissue  cell  (c  ft)  containing  here  only  one  corpuscle  with  an 
already  formed  capillary,  (a  and  c  from  a  new-born  rat,  6  from  a  fostal  sheep.) 

smaller  nuclei.  These  nuclei  soon  seem  to  round  them- 
selves, become  tinted  red  with  haemoglobin,  and  are  in  fact 
the  nucleated  red  corpuscles  of  the  embryo.  The  connective 


60  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

tissue  cells  in  which  by  a  nuclear  division  they  were  formed, 
elongate  very  rapidly  and  soon  touch  similar  elongations  of 
neighboring  tissue  cells.  Where  they  touch,  the  partition 
dividing  them  melts  away  and  the  cavities  of  the  cells  are 
converted  into  a  system  of  capillaries.  This  system  of 
capillaries  is  soon  connected  with  larger  blood  vessels  and 
so  these  nuclei  find  themselves  in  the  general  circulation 
at  once.  The  protoplasm  of  the  tissue  cell  becomes  liqui- 
fied and  helps  to  form  the  plasma  of  the  blood.  This 
intra-cellular  mode  of  development  of  red  blood  corpuscles 
does  not  continue  after  birth,  unless  it  be  in  animals  such 
as  the  rat,  which  are  born  in  a  very  immature  condition. 
For  this  reason  we  must  in  the  adult  body  seek  for  their 
origin  elsewhere. 

It  is  now  fairly  well  established  that  in  adult  life  they 
arise  in  the  red  marrow  of  the  bones.  In  this  red  marrow 
there  may  be  observed  corpuscles  which  seem  identical  with 
the  nucleated  red  corpuscles  of  the  embryo.  In  fact,  it 
seems  probable  that  the  nucleated  embryonic  corpuscles 
migrating  into  the  red  marrow  of  the  bones  have  been  the 
lineal  ancestors  of  the  nucleated  red  corpuscles  in  the  adult 
marrow.  These  corpuscles  seem  to  divide  like  ordinary 


<®  Q  fe 


Fig.  13.— H^EMATOBLASTS  IN  PROCESS  OF  DIVISION.    From  the  red  marrow  of  the  Guinea- 
pig.     (After  Schafer.) 

corpuscles,  possess  the  power  of  amoeboid  movement,  and 
differ  from  the  ordinary  white  corpuscles  apparently  in  little 
more  than  the  possession  of  the  haemoglobin.  These 
nucleated  red  corpuscles  form  the  ordinary  non-nucleated 
corpuscles  of  the  blood  by  having  the  nucleus  gradually 
atrophy  and  disappear.  In  fact,  according  to  some  observ- 
ers the  nucleus  is  said  to  be  extruded  from  the  corpuscle 
and  then  dissolved,  while  the  non-nucleated  body  is  carried 
away  by  the  blood  stream  as  a  newly  created  blood  cor- 
puscle. These  marrow  corpuscles  have  been  called  ery- 


THE    BLOOD.  61 

throblasts  or  more  frequently  haematoblasts.  The  view  is 
held  by  many  observers  that  these  hsematoblasts  are  not  the 
lineal  descendants  of  the  nucleated  red  corpuscles  of  the 
embryo,  but  are  being  regularly  derived  from  the  ordinary 
white  corpuscles  of  the  blood  found  in  the  marrow. 

8. —  Length  of  Life  of  Red  Corpuscles.  That  red  cor- 
puscles are  being  produced  daily  in  great  numbers  is 
evident  from  the  fact  that  so  many  are  destroyed  in  the 
spleen  and  liver.  The  coloring  matter  of  the  bile  is 
derived  from  disintegrated  red  corpuscles,  and  the  number 
of  corpuscles  required  to  colof  to  such  an  extent  the  large 
amount  of  bile  daily  eliminated  exceeds  calculation.  It  is, 
of  course,  not  possible  to  tell  how  long  a  red  corpuscle  will 
retain  its  vitality  and  properly  perform  the  functions  ascribed 
to  it,  but  there  are  reasons  to  believe  that  the  ordinary 
length  of  life  of  such  a  corpuscle  varies  from  three,  to  pos- 
sibly not  more  than  eight  or  ten  weeks.  To  replace  the 
entire  number  of  corpuscles  in  the  body  every  two  months 
means  a  daily  manufacture  of  them  by  the  billions.  In 
fact,  it  seems  a  little  like  a  fairy  story  to  be  told  that  for 
every  beat  of  the  pulse  nearly  twenty  millions  of  these 
organisms  die.  Such  a  wholesale  manufacture  of  them  is 
to  be  explained  by  the  rapidity  with  which  these  haemato- 
blasts are  supposed  to  divide.  The  older  view  that  red  cor- 
puscles were  directly  derived  from  the  white  ones,  or  from 
the  blood  tablets,  has  been  abandoned  as  not  at  all  in 
accordance  with  observed  facts.  The  red  or  blood-forming 
marrow  is  found  in  the  extremities  of  most  of  the  bones  of 
the  trunk,  and  in  the  bones  of  the  skull.  It  is  interesting 
that  when  the  blood -formation  process  is  very  active  the 
yellow  marrow  itself  may  be  changed  into  red  through  all 
the  bones. 

9. — The  Destruction  of  the  Red  Corpuscles.  The  fact 
that  corpuscles  are  short  lived  brings  up  naturally  the  ques- 
tion as  to  the  manner  of  their  destruction  and  elimination. 
As  the  pigments  of  the  bile  are  derived  from  broken 
down  corpuscles  there  is  no  doubt  that  many  of  them  are 


62  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

disintegrated  in  the  liver.  Just  in  what  manner  we  do  not 
know.  In  the  spleen,  too,  there  occur  so-called  blood-cor- 
puscle-containing cells,  that  is,  large  white  corpuscles  which 
seem  to  have  eaten  up  decrepid  corpuscles  and  to  be  in  the 
process  of  digesting  them.  Just  how  these  cannibal  cells 
are  able  to  single  out  worn-out  corpuscles  and  leave  normal 
ones  untouched  is  probably  accounted  for  by  the  fact  that 
old  corpuscles  are  sticky,  and  so  remain  attached,  while 
normal  ones  are  carried  on  with  the  blood  stream. 

THE  WHITE  OE  COLORLESS  CORPUSCLES. 

Much  less  numerous  than  the  red  are  the  white  cor- 
puscles of  the  blood.  These  corpuscles  may  be  taken  as 
types  of  a  living  cell,  possessing  in  some  degree  all  the 
properties  that  characterize  ordinary  one-celled  animals. 
As  given  before,  the  number  of  the  white  as  compared  with 
that  of  the  red  is  about  one  to  three  or  four  hundred.  They 
vary  much  in  size,  many  of  them  are  even  smaller  than 
the  red  corpuscles,  others  differ  but  little  from  them,  while 
the  larger  ones  measure  from  one  and  one-third  times 
to  twice  the  size  of  the  red.  They  possess  no  cell  wall,  but 
seem  composed  throughout  of  a  granular  kind  of  prote- 


Fig. 14.— FORMS  OF  A  WHITK  BLOOD  CORPUSCLE  SKETCHED  AT  INTERVALS  DURING  ITS 

AMCEBOID   MOVEMENTS. 

a.  Beginning  of  movement;  b,  formation  of  pseudopodia;  c,  the  nucleus  itself  changes 
its  form;  d,  the  corpuscle  at  last  dead. 


THE   BLOOD.  63 

plasm  in  which  is  imbedded  the  large,  clearly  discernible 
nucleus.  Their  most  remarkable  property  is  that  of  being 
able  to  throw  out  processes  called  pseudopodia  and  to  wan- 
der from  place  to  place  like  the  ordinary  fresh  water 
amoeba,  hence  these  motions  are  called  amoeboid.  By  vir- 
tue of  this  amoeboid  movement  the  white  corpuscles  are 
able  to  wander  through  the  spaces  between  the  tissues,  and 
even  to  bore  their  way  through  the  delicate  walls  of  the 
capillaries.  When  such  a  phenomenon  is  viewed  under  a 
microscope  it  is  seen  how  a  corpuscle  will  attach  itself  to 
the  side  of  the  capillary,  probably  by  virtue  of  its  natural 
stickiness.  Soon  there  is  seen  projecting  on  the  outside 
of  the  capillary  a  tiny  little  process  which  gradually  becomes 
larger  at  the  expense  of  the  corpuscle  until  finally  the  full 
corpuscle  has  thus  wedged  its  way  through.  This  phenom- 
enon of  wandering  out  of  capillaries  is  especially  marked 
in  the  early  stages  of  inflammation  when  the  holes  so  made 
through  the  capillaries  frequently  become  so  large  and  so 
numerous  as  to  permit  the  red  corpuscles  to  be  mechan- 
ically forced  through,  and  thus  for  the  blood  itself  to  seep 
into  the  tissues,  hence  no  doubt  the  redness  and  the  swell- 
ing of  the  inflammation.  By  virtue  of  this  movement  they 
are  further  able  to  pick  up  foreign  particles  by  flowing 
around  the  particle  until  it  is  included  in  the  cell,  a  method 
exactly  similar  to  that  of  the  amoeba  when  it  secures  its 
food.  Foreign  particles  are  thus  literally  eaten  up  by  these 
cells. 

As  mentioned  in  a  previous  chapter,  it  is  highly  prob- 
able that  bacteria  which  find  their  way  into  the  blood  are 
thus  mechanically  picked  up  and  so  rendered  harmless. 
Particles  injected  into  the  blood  of  transparent  animals, 
such  as  the  water  flea,  being  picked  up  by  the  colorless 
corpuscles  of  the  blood,  may  be  watched  under  the  micro- 
scope. They  probably  serve  in  the  disintegration  of  old 
tissues,  for  it  is  possible  to  find  in  the  blood  of  some 
amphibians  when  they  are  losing  their  tails,  such  as  the 
change  from  the  tadpole  to  the  frog,  some  of  these  cells 


64  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

actually  containing  bits  of  muscle  and  nerve  of  the  disin- 
tegrated organ.  Being  thus  able  to  wander  up  and  down 
the  avenues  of  the  body,  in,  between,  and  through  the  tis* 
sues,  they  have  been  called  wandering  cells.  For  this 
reason  these  corpuscles  are  not  at  all  confined  to  the 
blood,  but  occur  with  a  similar  frequency  in  lymph,  in  the 
marrow  of  bones,  and  probably  the  so-called  connective 
tissue  corpuscles  are  but  slightly  differentiated  white  cor- 
puscles. Their  migration  in  the  formation  of  pus  has  been 
mentioned  in  a  preceding  chapter. 

It  seems  probable  that  these  corpuscles  are  instrumental 
in  absorbing  the  fat  from  the  intestines  by  mechanically 
carrying  it  from  the  villi  into  the  lacteals,  while  the  fat  cir- 
culating in  the  body  which  is  not  needed  by  the  tissues  is 
carried  by  such  corpuscles  and  stored  away  in  different 
parts  forming  adipose  tissue.  Such  fat-eating  cells,  some- 
times called  plasma  cells,  may  become  so  distended  with 
fat  that  the  cell  body  is  reduced  to  a  slight  envelope  sur- 
rounding the  huge  fat  globule.  White  corpuscles  possess  the 
power  to  multiply  by  the  process  of  ordinary  cell  division. 
This  may  occur  any  place  in  the  body,  e.  g.  in  the  blood, 
but  more  regularly  occurs  in  what  are  known  as  lymphatic 
glands . 

Lymphatic  glands  are  not  glands  in  any  true  sense  of 
that  term,  but  are  large  aggregations  of  white  corpuscles 
housed  in  a  capsule  of  connective  tissue.  The  fact  that 
through  such  capsules  lymphatic  vessels  flow,  has  given 
them  the  name  of  lymphatic  glands.  In  these  glands  the 
cells  grow  and  divide,  and  by  the  lymph  stream  circulating 
through  it  the  additions  are  carried  out  into  the  body.  Such 
lymphatic  glands  are  familiar  to  us  as -the  tonsils,  the  thy- 
mus  gland,  the  patches  of  Peyer,  and  numerous  little  lym- 
phatic nodules  distributed  all  over  the  body.  In  the  spleen, 
too,  these  corpuscles  seem  to  be  formed  in  an  analagous 
way. 

The  fate  of  these  corpuscles  is  difficult  to  determine  in 
all  cases.  There  is  reason  to  believe  that  in  addition  to  the 


THE    BLOOD. 


65 


cells  which  are  lost  in  the  formation  of  pus,  worn-out  cor- 
puscles are  sent  to  the  spleen  and  the  liver  to  be  disinte- 
grated. That  these  white  corpuscles  may  take  part  in  the 


a.L. 


\ 


tr. 


Fig.  15.— LYMPHATIC  GLAND,  DIAGRAMMATIC  SECTION.     (After  Sharpey.) 
«,  I,  lymphatic  running-  into  gland;    e,  I,  same  issuing;  C,  connective  tissue  capsule; 
M,  tr,  connective  tissue  ground  work;  I,  s,  lymph  space;  corpuscles  indicated  in  part  of 
gland  only. 

formation  of  new  tissues  and  so,  becoming  differentiated, 
become  muscle  or  connective  tissues,  or  whatever  tissue 
needed,  is  stated  by  many  observers  but  denied  by  others, 
and  future  investigation  must  settle  the  dispute.  The  rela- 
tion of  these  corpuscles  to  the  coagulation  of  blood  is  men- 
tioned in  the  discussion  of  that  process. 

THE  BLOOD  PLATES. 

Recently  attention  has  been  called  to  a  third  corpuscle  of 
the  blood,  the  blood  plates,  blood  tablets,  or  blood  plaques. 
These  are  corpuscles  much  smaller  than  the  red  corpuscles, 
are  pale  or  colorless,  and  in  shape  vary  from  the  round  to 
the  decidedly  oval  form.  Their  number  has  been  given  by 
5 


66  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

observers  as  varying  from  eighteen  thousand  to  twenty-five 
thousand  in  a  cubic  millimeter  of  blood.  They  break  down 
with  remarkable  rapidity  as  soon  as  blood  is  shed,  and  this 


Fig.  16.— BLOOD  CORPUSCLES  AND  PLATELETS  IN  A  SMALL  VEIN  OF  THE  RAT'S  MESEN- 
TERY.    (After  Osier.) 

probably  may  account  for  the  fact  that  they  were  only  re- 
cently discovered.  Just  where  these  come  from  is  still  a 
matter  of  question.  By  some  they  are  believed  to  be  merely 
parts  of  disintegrated  white  corpuscles,  but  as  they  have 
been  observed  in  the  circulating,  unharmed  blood,  this  view 
is  probably  not  correct.  Possibly  they  are  nothing  more 
than  very  small  white  blood  corpuscles.  A  very  important 
role  has  been  assigned  to  these  little  plates,  because  it  is 
believed  by  a  number  of  physiologists  of  rank  that  in  the 
disintegration  of  these  plates  the  fibrin  ferment  is  formed, 
which  starts  the  coagulation  of  the  blood.  The  fact  that 
they  disintegrate  so  rapidly  when  the  blood  is  put  under  an 
abnormal  condition  may  be  for  the  purpose  of  setting  going 
at  once  this  process  of  coagulation. 

Historical. — The  colorless  corpuscles  were  discovered  by  Hewson,  and 
their  amoeboid  motions,  in  the  case  of  human  corpuscles,  by  Davaine  in  1850. 
The  blood  tablets  were  first  described  by  Bizzozero. 

THE  BLOOD  PLASMA. 

The  liquid  part  of  the  blood  is  called  the  blood  plasma. 
When  the  corpuscles  are  removed  from  it  it  has  a  clear, 
slightly  yellowish  color,  a  rather  insipid  sweetish  taste,  is  a 
little  alkaline  in  its  reaction,  and  of  a  specific  gravity  a  little 
greater  than  water.  Its  most  striking  property  is  its  power 
to  form  in  a  rather  short  time  a  so-called  clot,  and  a  thor- 
ough understanding  of  the  composition  of  this  liquid  must 
be  preceded  by  a  discussion  of  the  process  of  coagulation. 


THE  BLOOD.  67 

THE  COAGULATION  OF  THE  BLOOD. 

It  is  a  matter  of  common  observation  that  when  the  blood 
is  allowed  to  stream  from  a  severed  vessel  into  a  jar  it  forms 
in  a  very  short  time  a  solid,  trembling  jelly.  This  happens 
in  the  blood  of  a  pigeon  almost  instantaneously;  in  the 
blood  of  a  horse,  coagulation  is  slower,  while  in  man  it  is 
medium.  Soon  the  top  of  the  jelly  or  clot  becomes  cupped, 
and  a  transparent  or  slightly  colored  liquid  appears  over  it. 
This  cupping  is  due  to  the  contraction  of  the  clot,  which, 
continuing,  soon  pulls  the  clot  loose  from  the  walls  of  the 
vessel,  and  by  its  continued  contraction  forces  out  larger 
and  larger  quantities  of  the  liquid  just  referred  to,  which  is 
called  serum.  If  the  blood  had  been  prevented  from  clot- 
ting so  rapidly,  which  might  have  been  done  by  subjecting 
it  to  a  cold  temperature,  the  corpuscles  would  have  settled 
to  the  bottom,  leaving  a  clear  liquid  on  top.  As  the  white 
corpuscles  are  not  quite  as  heavy  as  the  red,  they  are  the 
last  to  settle,  and  there  is  formed  a  whitish  layer  over  the 
top  called  the  "buffy  coat." 

As  soon  as  the  temperature  is  raised  the  blood  begins  to 
clot.  If  blood,  however,  as  it  is  streaming  into  the  jar  be 
stirred  with  a  stick,  or  as  we  say,  "whipped,"  it  does  not 
clot  regularly  at  all ;  but  there  may  be  seen  collected  on  the 
stick  a  bundle  of  threads  whose  removal  from  the  clot  has 
prevented  the  "blood  from  solidifying.  If  these  threads  be 
removed  from  the  stick  and  carefully  washed  to  free  them 
from  entangled  corpuscles,  they  are  seen  to  consist  of  a 
mass  of  stringy  matter  which  has  been  called  fibrin.  Evi- 
dently the  clotting  of  the  blood  is  due  to  the  fonnati6n  of 
these  threads  all  through  the  clot,  in  the  meshes  of  which 
threads  the  corpuscles  are  mechanically  included.  The 
later  contraction  of  these  threads  squeezes  out  the  con- 
tained serum.  The  difference,  therefore,  between  blood 
plasma  and  blood  serum  is  the  absence  of  the  fibrin  from 
the  latter.  Just  from  what  this  fibrin  comes,  and  what  are 
the  causes  that  have  led  to  its  sudden  formation  are  ques- 
tions for  further  study. 


68  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

Without  going  into  the  many  controversies  of  this  prob- 
lem, the  most  generally  accepted  theory  is  here  given  in 
explanation  of  coagulation ;  but  it  must  be  remembered  that 
many  points  are  not  yet  clear,  and  that  the  observations  of 
the  future  may  materially  change  our  present  notion.  Ac- 
cording to  the  observations  of  Alexander  Schmidt,  later 
modified  by  Hammarsten,  there  are  in  the  blood  three  main 
albumens.  These  are  fibrinogen,  fibrinoplastin,  sometimes 
called  paraglobulin,  and  serum  albumen.  The  serum 
albumen  takes  no  part  in  the  coagulation,  and  its  purpose 
in  the  blood  is  to  afford  a  nutritive  substance  for  the  tissues. 
If  the  blood  plasma  had  no  other  function,  this  one  albumen 
would  no  doubt  suffice  as  a  food  for  all  cells  of  the  body ; 
but  as  serum  albumen  clots  only  when  subjected  to  the 
action  of  heat  or  strong  chemical  reagents  the  coagulation  of 
the  blood  would  be  impossible,  and  the  danger  from  hem- 
orrhages would  be  always  imminent.  To  prevent  this  loss 
of  blood  other  albumens  are  added.  Of  these,  fibrinogen 
possesses  the  property  of  being  easily  changed  into  fibrin 
under  certain  definite  conditions.  To  follow  these  suc- 
cessive stages  in  detail  let  us  imagine  the  finger  suddenly 
cut.  As  soon  as  the  incision  is  made  into  the  flesh  and  the 
vessels  traversing  it,  the  blood  finds  itself  in  an  abnormal 
condition  and  the  blood  tablets  at  once  begin  to  disinte- 
grate, no  doubt  because  they  are  not  able  to  live  under  the 
changed  environment.  In  their  disintegration  they  form  a 
substance  which  is  called  fibrin  ferment.  This  fibrin  fer- 


Fig.   17. — NETWORK  OF  FIBRIN  THREADS  RADIATING  FROM  SMALL  CLUMPS  OF  BLOOD- 
PLATELETS.     (After  Schafer.) 

ment  at  once  reacts  upon  the  fibrinogen,  causing  that  to 
change  into  fibrin,  and  thus  a  clot  arises.  A  somewhat 
analagous  case  might  be  cited  in  the  curdling  of  milk  by 


THE    BLOOD.  69 

means    of    the    ferment   known  to  every  cheese-maker    as 
"  rennet."     If  a  little  of  this  rennet  be  added  to  even  large 
quantities  of  milk,  in  a  very  short  time,  by  the  action  of 
this  ferment,  the  milk  curds.     It  has  not  been  possible  to 
get  fibrin  ferment  pure,  but  neither  have  we  been  able  as 
yet  to  get  rennet  in  a  similar  form.     This  fibrin  ferment  is 
probably  not  produced  in  a  purposive  way  by  the  tablets, 
but  results  as  a  mere  element  of  disintegration  when  they 
die.     Thus  the  strings  of  fibrin  in  the  clotted  blood  existed 
in  the  normal  blood  in  the  form  of   the  liquid,  fibrinogen. 
This  liquid  did  not  change  into  fibrin,  because  no  fibrin  fer- 
ment is  present  in  normal  blood,  for  the  reason  that  the 
blood  plates  do  not  disintegrate   under    such  normal  con- 
ditions.    It  has  been  noted,  though,  that  if  a  solution  con- 
taining such  a  ferment  be  injected  in  considerable  quantities 
into  the  veins  of  an  animal,  internal  coagulation  at  once  re- 
sults.    The  presence  of  fibrinoplastin  seems  to  facilitate  this 
process,  although  it  takes  no  direct  part  in  it,  for  the  blood 
serum  has  as  much  fibrinoplastin  as  it  had  before  the  clot- 
ting took  place.     Just  how  the  substance  may  facilitate  a 
chemical  process  without  directly  taking  part  in  it  does  not 
seem   clear,  but   chemistry  offers  a    number  of    analogies. 
Fibrinogen  will  not,  however,  change  into  fibrin,  even  in 
the  presence  of  the  fibrin  ferment,  unless  there  be  found  in 
solution  in  it  certain  salts,  especially  common  salt  and  the 
salts  of  lime.     If  by  adding  a  little  oxalic  acid  the  lime  salts 
are  removed  from  fresh  blood  it  does  not  coagulate  at  all. 
This  fact  has  led  some  observers  to  believe  that  the  fibrin 
was  really  a  compound  of  the  fibrinogen  and  the  calcium,  a 
calcium-fibrinogenate. 

Possibly  this  matter  of  coagulation  may  more  easily  be 
understood  by  following  the  method  of  making  an  artificial 
clot.  If  a  solution  of  pure  fibrin,  such  as  may  be  secured 
from  a  hydrocele  fluid,  be  put  in  a  vessel,  it  will  not  coagu- 
late instantaneously  at  all.  If  now  to  this  fibrinogen  traces 
of  common  salt  and  lime  salts  be  added,  and  then  some 
fibrin  ferment  introduced,  it  will  begin  to  coagulate  at  once, 


70  STUDIES    IN  ADVANCED    PHYSIOLOGY. 

and  the  clot  seems  in  every  way  a  typical  normal  blood  clot. 
If,  however,  some  fibrinoplastiu  had  also  been  added,  the 
clot  would  have  formed  a  little  more  quickly,  but  the  final 
product  would  not  have  differed  from  the  first  in  any  notice- 
able way. 

The  question  naturally  arises  why  blood  does  not  coagu- 
•'  late  in  the  body?  If  a  blood  vessel  be  removed  from  the 
body  and  the  ends  tied,  the  blood  will  not  clot  for  hours. 
In  fact,  it  is  possible  to  cut  out  a  turtle's  heart  and  have 
the  blood  remain  liquid  in  it  for  seven  or  eight  days,  and 
yet  such  blood  when  exposed  in  many  other  ways  begins  to 
clot  at  once.  Some  have  tried  to  ascribe  to  the  lining  of 
healthy  blood  vessels  a  sort  of  inhibitory  function,  but  this 
is  a  mere  explanation  of  words  and  not  of  ideas.  The  point 
remains  that  for  some  yet  unexplained  reason  the  fibrin 
ferment  does  not  seem  to  have  been  produced,  possibly 
because  the  blood  plates  and  corpuscles  have  not  been  dis- 
integrated in  a  way  calculated  to  produce  this  ferment. 
Such  abnormal  conditions  as  a  bruised  blood  vessel,  expos- 
ure to  the  air,  contact  with  foreign  bodies,  serve  to  disinte- 
grate them  and  so  start  the  process  of  coagulation. 

While  in  the  discussion  so  far  the  formation  of  the  fibrin 
ferment  has  been  attributed  to  the  blood  plates,  there  is 
little  doubt  but  that  the  white  corpuscles  as  well,  in  their 
disintegration,  form  this  fibrin  ferment.  This  may  explain 
why  in  certain  diseases  of  the  body  in  which  corpuscles 
disintegrate  in  large  numbers  internal  clots  have  been 
formed,  interrupting  the  circulatory  course  and  so  causing 
death.  It  is  not  an  infrequent  observation  too  that  in  per- 
sons suffering  from  blood  poisoning,  a  disease  in  which 
large  quantities  of  corpiiscles  are  lost,  there  is  a  tendency 
towards  the  formation  of  internal  clots,  which  frequently 
prove  fatal  before  the  full  effects  of  the  blood  poisoning  have 
had  time  to  arrive.  In  fact,  in  fevers  generally  the  amount 
of  fibrin  ferment  in  the  blood  seems  a  little  more  abundant. 
While  in  the  daily  life  of  a  healthy  individual  many  such  cor- 
puscles disintegrate,  they  do  not  do  so  in  sufficient  numbers 


THE   BLOOD.  71 

to  form  material  amounts  of  fibrin  ferment,  and  so  the 
blood  is  prevented  from  clotting.  Though  this  explanation 
at  first  sight  seems  sufficient,  a  closer  study  shows  that  it 
does  not  yet  answer  all  the  observed  facts  in  coagulation  of 
blood,  and  there  are  many  observers  who  offer  modified 
theories  to  account  for  this  phenomenon.  Thus,  we  do  not 
know  from  what  source  the  fibrinogen  is  derived.  Al. 
Schmidt,  the  originator  of  the  theory  here  given,  believes 
that  the  fibrinogen  and  the  fibrinoplastin  both,  as  well  as 
fibrin  ferment,  are  derived  from  the  disintegration  of  white 
corpuscles.  This  might  explain  why  at  the  point  where 
clotting  begins  and  where,  therefore,  large  numbers  of 
these  corpuscles  are  dissolved,  added  amounts  of  fibrinogen 
should  form  and  thus  facilitate  clotting. 

But  to  recapitulate :  The  best  explanation  now  available 
is  that  there  is  present  in  normal  human  blood  dissolved  in 
the  plasma  about  two-tenths  per  cent,  of  an  albumen  known 
as  fibrinogen.  This  fibrinogen  in  the  presence  of  common 
salt  and  lime  salts  will  change  into  insoluble  fibrin  threads 
under  the  influence  of  this  fibrin  ferment,  at  present  believed 
by  all  to  be  derived  from  the  colorless  corpuscles  of  the 
blood.  The  property  of  coagulation  is  by  no  means  pecu- 
liar to  fibrinogen.  Most  albumens  possess  it  more  or  less 
fully  shown.  The  liquid  casein  of  milk  easily  coagulates 
into  cheese  under  the  action  of  the  rennet  ferment.  The 
liquid  albumen  of  living  muscles  soon  clots  after  death, 
producing  the  so-called  death  stiffening,  or  rigor-mortis. 
Even  ordinary  egg  albumen  can  easily  be  made  to  coagu- 
late by  the  action  of  heat  or  chemical  agents. 

The  liquid  that  is  left  after  the  blood  has  clotted  is 
called  serum. 

THE  COMPOSITION  OF  SERUM. 

The  serum  of  ordinary  blood  contains  about  ninety  per 
cent,  of  water.  It  contains  two  albumens  which  have  indi- 
rectly taken  part  in  the  formation  of  the  clot  called  fibrino- 
plastin and  serum  albumen.  This  serum  albumen  must  not 


72  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

be  confused  with  the  serum  itself.  Serum  is  the  name 
applied  to  the  entire  liquid  after  the  fibrinogen  has  been 
removed  in  the  form  of  fibrin,  while  serum  albumen  is  but 
one  of  the  albumens  found  in  this  liquid.  Fibrinoplastin,  so 
called  by  Al.  Schmidt,  and  called  paraglobulin  by  Kiihne, 
is  present  to  the  amount  of  about  one  per  cent.  The  serum 
albumen  forms  four  or  five  per  cent.  These  two  albumens 
are  insoluble  in  pure  water,  but  are  soluble  in  water  con- 
taining a  little  common  salt,  which  latter  accounts  for  their 
being  in  solution  in  normal  blood.  The  two  differ  but  very 
little  from  each  other,  but  they  may  be  separated  if  to  a 
solution  of  serum  at  a  temperature  of  about  ninety-five 
degrees  Fahrenheit,  crystals  of  magnesium  sulphate  be 
added  to  saturation.  The  fibrinoplastin  is  by  this  process 
precipitated  out  of  the  solution. 

As  stated  before,  the  serum  albumen  is  the  main  nutri- 
tive factor  of  the  blood.  It  is  almost  identical  with  liquid 
egg  albumen,  and  differs  from  it  only  in  its  reaction  with 
certain  chemical  agents.  It  is  this  albumen  which  in 
pathological  conditions  of  the  kidneys,  such  as  Bright 's 
disease,  is  eliminated  in  the  excretion.  Both  serum  albu- 
men and  fibrinoplastin  may  be  made  to  coagulate  if  blood 
serum  be  heated  to  a  temperature  of  about  one  hundred 
and  seventy-six  degrees  Fahrenheit. 

The  serum  further  contains  traces  of  fat  in  the  form  of 
fine  granules,  to  the  amount  of  about  one-half  per  cent. 
After  a  diet  rich  in  fats  the  amount  may  reach  one  per 
cent.  Traces  of  grape  sugar  in  amounts  varying  from  one- 
tenth  to  three-tenths  of  a  per  cent,  occur.  This  amount 
may  also  greatly  vary  with  a  diet  rich  in  sugars.  It  further 
contains  in  very  small  amounts  a  number  of  organic  nitrog- 
enous compounds,  such  as  kreatin,  urea,  and  uric  acid, 
substances  with  which  we  shall  be  further  concerned  in  the 
discussion  of  assimilation  and  nutrition.  The  mineral  salts 
are  represented  in  an  amount  reaching  not  quite  one  per 
cent.  Of  these  common  salt,  or  sodium  chloride,  forms 
more  than  half,  and  sodium  carbonate  a  good  portion  of  the 


THE   BLOOD.  73 

remainder.  It  is  an  interesting  fact  to  note  that  while  the 
potassium  salts  are  contained  so  largely  in  the  corpuscles, 
the  sodium  salts  figure  in  a  similar  role  in  the  liquid.  A 
yellow  pigment  of  a  nature  not  understood,  and  traces  of  a 
substance  to  which  the  characteristic  odor  of  blood  is  due, 
finally  complete  the  list  of  things  which  enter  into  the  com- 
position of  blood.  There  are,  of  course,  dissolved  in  the 
blood  certain  gases,  but  the  discussion  of  these  is  post- 
poned to  the  chapter  on  respiration. 

In  the  discussion  of  blood,  that  of  lymph  is  naturally 
included,  lymph  being  in  fact  nothing  but  the  plasma  of 
the  blood  which  has  by  osmotic  processes  soaked  through 
the  walls  of  the  capillaries  and  so  bathed  the  tissues.  To 
use  an  arithmetical  expression,  lymph  is  blood  minus  the 
red  corpuscles.  White  corpuscles  are  present  in  lymph 
owing  to  the  fact  that  they  are  able  to  pass  through  the 
capillary  walls,  and  in  general  are  able  to  wander  among 
the  tissues.  Occurring  so  plentifully  in  lymph,  has  given 
to  them  the  name  by  which  they  are  frequently  called,  that 
of  lymph  corpuscles.  It  is  well  to  keep  in  mind  that  the 
migration  of  these  corpuscles  through  the  walls  of  the  capil- 
laries, as  it  is  normally  done,  does  not  necessarily  injure 
them.  Probably  they  press  their  way  through  tiny  open- 
ings made  between  the  cells  which  form  the  capillary  wall. 
In  any  case  the  opening  made  is  so  small  that  it  is  at  once 
closed  up. 

THE  PHENOMENON  OF  OSMOSIS. 

The  phenomenon  of  osmosis  referred  to  so  frequently  in 
physiological  discussion  is  the  phenomenon  of  the  diffusion 
of  liquids  through  a  membrane  in  such  a  way  that  the  com- 
positions of  the  two  liquids  tend  to  become  similar.  Thus, 
if  a  moist  animal  membrane,  such  as  a  stretched  bladder, 
be  taken  and  placed  so  as  to  divide  a  vessel  in  two  compart- 
ments, and  then  water  containing  sugar  be  placed  in  one 
compartment,  and  salty  water  in  another,  osmotic  currents 
are  soon  set  up  through  the  membrane,  by  means  of  which 


74  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

/ 

part  of  the  sugar  is  carried  to  the  salty  side  and  part  of  the 
salt  to  the  sugary  side.  These  currents  continue  so,  sec- 
ondary causes  not  preventing,  until  the  proportion  of  sugar 
and  salt  are  the  same  throughout.  In  an  exactly  sim- 
ilar way  the  plasma  of  the  blood  containing  in  solution  a 
number  of  nutritive  substances  passes  through  the  wall  of 
the  capillary  into  and  between  the  tissues,  where  these 
nutritive  substances  are  being  continually  taken  up  by  the 
tissues,  and  so  an  equilibrium  never  established.  On  the 
other  hand,  a  number  of  waste  products  which  are  formed 
in  the  tissues  pass  into  the  blood. 


CHAPTER  VI. 


THE  SUPPORTING  TISSUES. 

The  supporting  tissues  are  comprised  of  those  tissues 
which  give  support  to  the  delicate  organs  of  the  body  and 
their  component  cells.  They  are  distributed  throughout  the 
entire  body  and  give  form  and  shape  to  the  same.  Includ- 
ing all  the  connective  tissues  and  not  merely  the  bony 
skeleton,  these  supporting  tissues  would  preserve  the  actual 
size,  appearance,  and  contour  of  the  body,  even  if  every 
vestige  of  their  tissues  could  be  removed.  The  body  with 
nothing  but  its  system  of  supporting  tissues  would  remain 
apparently  so  unaltered  that  the  absence  of  all  the  vital 
parts  might  not  even  be  suspected  by  the  observer. 

The  supporting  tissues  naturally  fall  into  four  divisions : 
First,  the  osseous;  second,  the  cartilaginous;  third,  the 
connective;  and  fourth,  the  humors.  All  of  these  tissues 
are  alike,  in  the  fact  that  they  are  formed  not  out  of  cells, 
but  from  the  product  of  cells,  somewhat  in  the  way  in 
which  a  cobweb  is  formed — not  out  of  spiders,  but  as  the 
product  of  their  secretion.  Not  being  made  up  of  living 
cells,  therefore,  these  tissues  are  in  a  sense  dead  matter, 
although  the  cells  that  produce  them  frequently  remain  in 
the  tissue,  forming  a  very  integral  part  of  its  structure. 
The  cells  that  produce  bone  are  called  bone  corpuscles,  or 
osteoblasts;  the  cells  that  form  cartilage  are  the  cartilage 
cells,  or  chondrioblasts ;  those  that  form  the  connective 
tissues  and  the  humors  are  called  connective  tissue  cor- 
puscles. All  of  these  cells  resemble  very  closely  the  white 
corpuscles  of  the  blood,  and  are  probably  nothing  but 
slightly  differentiated  cells  set  apart  for  the  purpose  of 
secreting  and  maintaining  the  supporting  frame-work  of 
the  body. 

(75) 


76 


STUDIES   IN   ADVANCED   PHYSIOLOGY, 


Fig.  18.— THE  ENTIRE  SKELETON. 

a,  6,  skull;  c,  cervical  vertebrae;  d,  sternum;  e,  lumbar  vertebrae;  /,  ulna;  g,  radius; 
h,  carpal  bones;  i,  metacarpal  bones;  A-,  phalanges ;  I,  tibia;  w,  fibula;  n,  tarsal  bones; 
o,  metatarsal  bones;  P,  phalanges;  ry,  patella;  r,  femur;  S,  os  innominatnm;  t,  humerus; 
u,  clavicle. 


THE   SUPPORTING  TISSUES. 


77 


Bony  Tissue. 

Osseous  tissue  is  familiar  to  every  one  as  the  tissue  of 
which  bone  is  composed.  The  bones  of  the  body  in  their 
proper  articulations  form  the  skeleton.  The  skeleton  con- 
sists of  a  trunk,  two  pairs  of  extremities,  their  supporting 
girdles,  and  the  skull. 

The  trunk  is  composed  of  seven  cervical  vertebrae,  twelve 
dorsal,  five  lumbar,  the  sacrum,  and  the  coccyx. 

VERTEBRA. 

The  first  vertebra  called  the 
atlas  differs  from  the  rest  in  that 
the  body  of  the  atlas  has  grown  to 
the  next  vertebra,  the  axis,  forming 
a  pivot,  the  odontoid  process  on 
which  the  head  turns.  The  cervi- 
cal vertebra  has  a  few  characteris- 
tics by  means  of  which  it  may  be 


Cot) 

4V 

Fig.  19.— SPINAL  COLUMN. 

(vSide  view.) 

(',  cervical;  D,  dorsal;  L, 
lumbar;  S,  sacrum;  Co, 
coccyx. 


Fig.  20.— ATLAS.     (Seen  from  above.) 
Dotted  lines,  position  of  transverse  ligament  to 
hold  in  place  the  odontoid  process ;  oblique  line,  in- 
sertion of  ligament  into  a  bony  tubercle;  other  lines, 
articulating  surfaces. 


Fig.  21. — ATLAS  AND  AXIS,  FRONT  VIEW. 
Upper  line,  odontoid  process;  remaining  lines, 
articulating  processes. 


78 


STUDIES   IN   ADVANCED    PHYSIOLOGY. 


Fig.  22.— A  TYPICAL  CERVICAL  VERTEBRA. 

Showing  intra-vertebral  foramen  and  bifid  spinous  process. 

recognized.  Its  spinous  process  is  bifid,  and  the  transverse 
process  appears  with  an  opening  called  the  intra-vertebral 
foramen.  Through  this  the  intra-vertebral  artery  ascends 
to  the  brain.  This  is  not  really  a  hole  through  the  trans- 
verse process  of  the  cervical  vertebra,  but  is  a  space  left 
between  the  transverse  process  and  the  stump  of  a  rib  which 
is  fused  with  it,  there  being  in  early  life  indications  of  the 
presence  of  ribs  throughout  the  cervical  region.  The  dorsal 
vertebrae  are  at  once  recognized  in  having  the  articulating 
facets  for  the  ribs,  and  in  having  their  spinous  processes 


Fig.  23.— A  DORSAL  VERTEBRA  FROM  THE 
RIGHT  SIDE. 

Two  upper  lines,  facets  for  the  articula- 
tion of  ribs;  left  line  below,  inferior  articular 
process;  middle  line  below,  vertebral  notch 
(exit  of  nerves,  etc.) ;  right  line  below,  facet 
for  lower  rib. 


Fig.  24. — I,TTMBAR  VERTEBRA  FROM 
ABOVE. 

t'pper  line,  inferior  articulating  pro- 
cess; lower  line,  superior  articulating 
process. 


THE   SUPPORTING   TISSUES. 


79 


drawn  downward.  This  latter  arrangement  is  better  adapted 
for  the  attachment  of  the  heavy  muscles  of  the  body.  The 
lumbar  vertebrae  have  proportionately  a  much  larger  body, 
and  the  processes  relatively  much  shorter  and  thicker.  The 
sacrum  consists  in  reality  of  five  fused  vertebrae,  the  indi- 
vidual ones  being  still  clearly  traceable  on  it.  This  fusion 


SUP.  ARTIE.    PHOC. 


Fig.  25.— THE  SACRUM,  FRONT  VIEW. 

aids  materially  in  giving  strength  to  that  portion  of  the  col- 
umn where  it  is  connected  with  the  hip  bone.  The  coccyx 
consists  of  from  two  to  four  or  five  very  much  reduced  verte- 
brae and  serves  as  far  as  we  know  no  special  function.  The 
individual  vertebrae  are  separated  by  pads  of  elastic  carti- 
lage which  give  them  a  certain  amount  of  lateral  motion, 
and  which  also  serve  as  cushions  to  break  the  jars.  The 
double  curvature  of  the  entire  column  still  further  serves  to 
reduce  this  to  a  minimum. 


BIBS. 

Attached  to  the  dorsal  vertebrae  are  twelve  pairs  of  ribs, 
which  extend  slightly  downward,  then  upward,  and  enclose 
the  organs  of  the  chest.  With  the  exception  of  two  on  each 
side,  called  the  floating  ribs,  they  are  attached  to  the  ster- 
num, or  breast  bone,  by  means  of  elastic  cartilages,  which 
permit  a  slight  movement  at  these  points. 


80  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

PECTOEAL  AND  PELVIC  GIEDLES  AND  THE  EXTREMITIES. 

More  or  less  firmly  attached  to  this  trunk  are  the  two 
girdles  of  the  body,  the  pectoral  girdle,  supporting  the  arms, 
and  the  pelvic  girdle,  for  the  attachment  of  the  limbs.  The 
pectoral  girdle  consists  on  each  side  of  two  bones,  the 


Fig.  26.— RIGHT  CLAVICLE,  FROM  ABOVE. 


Fig.  27.— ANTERIOR  VIEW  OF  RIGHT 
SCAPULA. 


clavicle  and  the  scapula.  The  clavicle  articulates  with  the 
manubrium  of  the  breast  bone  and  with  the  large  acromion 
process  of  the  scapula.  This  serves  to  hold  the  shoulder 
back  in  place.  Animals  that  walk  on  their  four  limbs  have 
the  clavicle  reduced  to  a  mere  splint  or  thread  of  cartilage, 
as  it  would  be  in  their  case  undesirable  to  have  the  shoul- 
ders pitched  back.  This  reduction  of  the  clavicle  allows 
the  shoulders  of  these  animals  to  drop  under  the  body,  a 
position  much  better  suited  for  supporting  their  weight. 


THE   SUPPORTING   TISSUES. 


81 


The  scapula,  or  shoulder  blade,  is  not  connected  with 
the  back  bone,  but  lies  imbedded  in  the  muscles  of  the 
shoulder.  This  loose  attachment  aids  materially  in  giving 
freedom  of  motion  to  the  arm.  The  scapula  really  consists 
of  two  bones,  the  scapula  proper  and  the  coracoid  bone, 
which  latter,  however,  has  been  reduced  to  a  mere  process, 
which  has  grown  on  to  the  scapula,  and  which  is  called  the 
coracoid  process.  In  birds  this  coracoid  process  is  a  very 
large  and  distinct  bone,  and  serves  to  support  the  wings, 


CONDYLE 


Fig.  28.— THE  RIGHT  HUMERUS  FROM  BE- 
FORE. 


Fig.  29.— THE  BONES  OF  THE  RIGHT  HAND 

SEEN  FROM  BEFORE. 

*,  scaphoid;  I,  lunar;  c,  pyramidal;  P, 
pisiform;  t,  trapezium;  next,  the  trapezoid; 
then,  the  osmagnum;  u,  unciform;  /,  V, 
metacarpals;  1,2,3,  phalanges;  *,  sesamoid 
bones. 


while  the- clavicle  loses  its  attachment  with  the  breast  bone, 
and  meeting  the  clavicle  on  the  other  side  forms  the  so-called 
' '  wish  bone. ' '    Articulating  in  the  glenoid  fossa  of  the  scap- 
6 


82  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

ula  is  the  bone  of  the  forearm  called  the  humerus.  This 
articulates  at  the  elbow  with  two  bones,  the  radius  and  the 
ulna.  The  ulna  forms  the  main  articulation,  forming  really 
the  hinge  joint  of  the  elbow.  The  backward  process  on  the 
ulna,  which  prevents  the  backward  flection  of  the  elbow 
joint,  is  called  the  olecranon  process.  This  is  really  an 
elbow  cap,  similar  to  the  knee  cap,  which,  however,  in  this 
case  has  become  firmly  attached  to  the  ulna. 

At  the  wrist  the  radius  and  ulna  articulate  with  a  series 
of  eight  bones  called  the  carpal  bohes.  Here  the  radius 
forms  the  main  articulation,  and  by  rotating  around  the  ulna 
the  hand  is  pronated  and  supinated.  These  carpal  bones 
are  followed  by  five  metacarpal  bones,  to  which  in  turn  are 
connected  three  phalanges  for  each  finger,  the  thumb  hav- 
ing but  two.  The  radius  is  on  the  thumb  side  of  the  wrist. 


ISCHIUM 

Fig.  30.— RIGHT  os  INNOMINATUM. 


Attached  to  the  sacrum  on  each  side  is  the  os  innom- 
inatum,  so  called  because  the  early  anatomists  were  not 
able  to  name  it  after  any  object  they  knew.  This  bone 


THE    SUPPORTING   TISSUES. 


83 


really  consists  of  three  bones,  which  have  grown  together, 
the  large  flat  upper  ilium,  which  connects  with  the  sacrum, 
the  lower  ischium,  which  supports  the  weight  of  the  body 
in  a  sitting  posture,  and  the  forward  pubic  bone,  which  by 


Fig.  31.— ADULT  MALE  PELVIS,  SEEN  FROM  BEFORE.     (Upper.) 

ADULT  FEMALE  PELVIS,  SEEN  FROM  BEFORE.    (Lower.) 

(After  Allen  Thompson.) 


articulating  with  the  pubic  bone  on  the  other  side  forms  the 
front  wall  of  the  pelvis.  The  large  articulating  facet  for  the 
head  of  the  femur  is  called  the  acetabulum.  A  large  hole 
formed  through  the  bone,  the  thyroid  foramen,  serves  for 
the  exit  of  nerves  and  blood  vessels  from  the  pelvic  cavity. 
Attached  to  the  innominate  bone  is  the  femur,  the  long  bone 
of  the  thigh.  This  articulates  at  the  knee  with  the  tibia. 


84 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


Along  the  outside  of  the  tibia  and  serving  to  brace  this  ar- 
ticulating surface  with  the  femur  lies  the  smaller  fibula. 


MAUEOLUS 

Fig.  32.— RIGHT  TIBIA  AND  FIBULA,  FROM 


STYLOID  PROCESS 

Fig.  33.— RIGHT  RADIUS  AND  ULNA  IN  SUPI- 

NATION  OF  THE  HAND. 


At  the  ankle  the  tibia  articulates  with  the  astragalus, 
which,  however,  represents  two  of  the  tarsal  bones  grown 
together.  This  fusion  to  form  the  astragalus  explains  the 
presence  of  but  seven  tarsal  bones.  The  large  tarsal 
bone  forming  the  heel,  into  which  the  tendon  Achilles  is 
attached,  is  the  heel  bone,  or  os,calcaneum.  These  tarsal 
bones,  then,  connect  with  the  metatarsal,  which  are  in  turn 
followed  by  a  series  of  three  phalanges  for  each  toe,  and 
two  for  the  big  toe.  In  the  hands  and  feet,  especially  of 
persons  who  are  in  the  habit  of  doing  hard  manual  labor, 


THE    SUPPORTING    TISSUES. 


85 


there  are  developed  frequently  at  the  joints  small,  extra 
bones,  called  sesamoid  bones.  The  rather  large  knee  cap 
is  probably  nothing  more  than  such  a  sesamoid  bone,  which 


•nncwmup ' 
Fig.  34. — THE  RIGHT  FEMUR  FROM  BEHIND. 


Fig.  35.— THE  BONES  OF  RIGHT  FOOT,  SEEN 

FROM  ABOVE. 

A,  navicular  bone;  6,  astragalus;  c,  d, 
os  calcaneum;  e,  internal  cuneiform;  /, 
middle  cuneiform;  g,  external  cuneiform; 
h,  cuboid  bone;  1,  V,  metatarsals;  1,2,3, 
phalanges. 


has  finally  become  persistent.  Such  sesamoid  bones  prob- 
ably serve  to  lessen  the  friction  of  the  tendons  pulling  from 
the  joint. 

THE  SKULL. 

The  bones  of  the  skull  serve  to  enclose  the  brain  and  to 
give  support  to  the  face  and  its  organs.  The  bones  which 
enclose  the  brain,  or  cranium,  are  eight:  the  frontal,  two 
parietals,  two  temporals,  one  occipital,  one  sphenoid,  and  one 
ethmoid.  The  bones  which  serve  to  form  the  face  are  the 


86 


STUDIES    IN   ADVANCED    PHYSIOLOGY. 


two  nasal  bones,  the  two  lachrymal  bones,  two  malar  bones, 
the  upper  maxilla,  the  two  palatine  bones,  the  lower  maxilla, 


Fig.  36.— FRONT  VIEW  OF  MALE  SKULL  AT  ABOUT  TWENTY  YEARS.   (Allen  Thomson.) 

1,  frontal  eminence;  2,  glabella,  between  the  superciliary  ridges,  and  above  the  trans- 
verse suture  of  union  with  the  nasal  and  superior  maxillary  bones ;  3,  orbital  arch  near 
the  supraorbital  notch;  4,  orbital  surface  of  great  wing  of  sphenoid,  between  the  sphe- 
noidal  and  the  spheno-maxillary  fissures;  5,  anterior  nasal  aperture,  within  which  are 
seen  in  shadow  the  vomer  and  the  turbinate  bones;  6,  superior  maxillary  bone  at  the 
canine  fossa — above  the  figure  is  the  infraorbital  foramen;  7,  incisor  fossa;  8,  malar  bone; 
9,  symphysis  of  lower  jaw;  10,  mental  foramen;  11,  vertex,  near  the  coronal  suture;  12, 
temporal  fossa;  13,  zygoma;  14,  mastoid  process;  15,  angle  of  the  jaw;  16,  mental  pro- 
tuberance. In  this  skull  there  are  fourteen  teeth  in  each  jaw,  the  wisdom  teeth  not  hav- 
ing yet  appeared. 

the  vomer,  and  the  two  turbinates.  Suspended  by  cartila- 
ginous threads  from  the  temporal  bone  is  the  hyoid  bone, 
which  serves  to  give  support  to  the  muscles  of  the  tongue. 
It  is  entirely  impossible  to  give  any  satisfactory  descrip- 
tions, and  even  in  good  pictures,  any  adequate  notion  of  the 


THE   SUPPORTING   TISSUES. 


87 


arrangement  of  bones.  The  enumeration  of  the  bones  and 
the  cuts  here  given  are  intended 
to  serve  only  as  a  manual  in  the 
hands  of  the  student  who  is  for- 
tunate enough  to  have  an  actual 
skeleton  before  him  for  study. 
Detailed  descriptions  of  the  in- 
dividual bones  is  deemed  un- 
necessary, but  the  detail  given 
in  the  pictures,  together  with 


Fig.  37.— THE  HYOID  BONE. 


Z 


Fig.   38.— A  SIDE  VIEW  OF  THE   SKULL. 

O,  occipital  bone;  T,  temporal;  Pr, 
parietal;  F,  frontal;  S,  sphenoid;  Tsp, 
wing  of  sphenoid;  Z,  malar;  MX,  maxilla ; 
N,  nasal;  E,  ethmoid;  L,  lachrymal;  Md, 
inferior  maxilla. 


JMi 


the  accompanying  names,  ought  to  be  the  points  which  the 
student  should  verify  for  himself  on  every  bone  in  question. 


88 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


THE  MINUTE  STRUCTURE  OF  BONES. 

Little  need  be  said  concerning  the  gross  structure  of 
bones.  A  mere  glance  will  show  one  the  difference  between 
the  long  bones,  such  as  the  femur  or  hu~ 
merus,  the  short  bones,  such  as  those  of 
the  tarsus  and  carpus,  the  tabular  bones, 
like  the  parietal  bones  of  the  skull,  and  the 
irregular  bones,  which  do  not  seem  to  fit 
in  any  of  the  preceding  classes.  If,  fur- 
ther, a  long  bone,  such  as  the  humerus, 
say,  be  examined,  it  is  easily  seen  to  con- 
sist of  a  long  shaft  made  up  of  hard,  dense, 
apparently  homogeneous  bone,  with  some- 
what expanded  ends,  intended  for  articu- 
lating surfaces.  Numerous  little  holes  are 
visible,  through  which  blood-vessels  and 
nerves  enter  the  bone.  If  such  a  bone  be 
sawed  in  two  a  large,  empty  space  appears 
through  the  shaft,  known  as  the  medullary 
cavity.  It  is  filled  in  life  with  a  yellowish 
substance  consisting  mostly  of  fat,  called 
the  yellow  marrow.  At  the  end  the  bone 
is  seen  to  be  cancellated  or  spongy.  In 
this  cancellated  bone  is  found  the  red  mar- 
row, the  seat  of  the  formation  of  the  red 
corpuscles  of  the  blood.  Further  than  this 
nothing  can  be  made  out  as  to  the  struc- 

If  a  tabular 
bone  such  as  the  parietal    be    examined, 


Fig.  39.— THE  GROSS  AN-    A  .-1,1  •  -.     i 

ATOMY   OP  A  LONG  ture  with  the  unaided  eye. 

BONE.     (Humerus.) 

numerous   little  openings   into  it  for   the 
entrance    and    exit    of    blood-vessels 


a,    medullary 
containing  the  marrow; 
I,  shaft  of  hard  bone;  c, 
spongy    or    cancellated 


are 


bone;  d,  terminal  card-  aga|n  visible,  while  if  it  be  broken  it  shows 

that  it  is  made  up  of  two  plates,  the  denser 

bone   on  the  outside  and   an  intervening  layer  of    spongy 

bone  called  diploe.     The  structure  of  the  parietal  bone  is 


THE    SUPPORTING   TISSUES. 


89 


repeated  in  a  number  of  the  irregular  bones  of  the  body, 
which  have  on  the  outside  some  denser  bone,  while  the 
interior  is  more  or  less  spongy.  It  will  be  recalled  that 


Fig.   40.— LONGITUDINAL    SECTION   OF  THE   HEAD   OF   THE   FEMUR   SHOWING   THE   CANCEL- 
LATED  STRUCTURE  AT  END,  AND  SOLID  BONE    OF    SHAFT.        (From    a    photograph  by 

Zaaijer.) 


in  the  spongy  part  of  all  these  bones,  no  less  than  in  those 
of  the  long  bones,  red  marrow  occurs. 

To  discover  the  real  structure  of  bone  it  is  necessary  to 
grind  a  bone  into  an  exceedingly  thin  section,  so  that  it 
may  be  viewed  with  a  microscope.  If  such  a  cross  section, 


90 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


say  from  the  shaft  of  the  humcrus,  be  taken,  it  is  found  to 
be  not  homogeneous  at  all,  but  pierced  by  a  set  of  canals 
running  mainly  in  a  longitudinal  direction,  known  as  Haver- 
sian  canals.  Through  these  canals  run  blood-vessels,  nerves 


Fig.  41.— TRANSVERSE  SECTION  FROM  THE  SHAFT  OF  THE  HUMERUS,  SHOWING  THRKE 

HAVERSIAN  SYSTEMS  COMPLETE. 

The  Haversian  canals,  lacunae  and  canaliculi  appear  black,  being  filled  with  air  and 
debris  from  the  grinding. 


and  lymphatics.  Around  each  Haversian  canal  lie  from 
several  to  many  series  of  cylindrical  plates,  or  lamellae, 
between  which  occur  in  characteristic  rows  little  openings 
called  lacunae.  Running  out  from  each  lacuna  are  many 
divergent  and  branching  canals  called  canaliculi,  which 
connect  with  similar  canals  from  the  immediately  surround- 
ing lacunae.  The  canaliculi  of  the  lacunae  next  to  the 
Haversian  canal  open  into  the  Haversian  canal.  By  this 
system  of  lacunae  and  canaliculi  nourishment  may  soak 
from  the  Haversian  canal  through  every  portion  of  the  bone. 
These  lacunae  are  in  life  each  filled  by  a  little  corpuscle 
not  unlike  an  ordinary  white  blood-corpuscle,  called  an 
osteoblast.  Arms  from  these  osteoblasts  extend  through  the 


THE    SUPPORTING   TISSUES.  91 

canaliculi  and  come  in  contact  with  similar  arms  of  neigh- 
boring osteoblasts.  In  this  way  there  is  really  a  system  of 
direct  communication  between  the  living  parts  of  the  entire 


Fig.  42.— AN  OSTEOBLAST  IN  DETAIL. 

o,  the  wall  of  the  lacuna  where  the  bone  corpuscle  has  shrunk  away  from  it. 

vbone.  These  osteoblasts  are  the  agents  which  secrete  the 
bone  substance  surrounding  them,  somewhat  like  the  clam 
secretes  its  surrounding  calcareous  shell.  The  bone  sub- 
stance, or  the  matrix,  as  it  is  called,  appears  perfectly 
homogeneous,  but  with  proper  reagents  there  may  be 
brought  to  view  many  little  fibres  permeating  it  in  all 
directions.  These  fibres,  no  doubt,  add  materially  to  the 
strength  and  consistency  of  the  bone,  somewhat  as  the 
hairs  frequently  mixed  with  mortar  materially  serve  to  keep 
that  from  crumbling.  These  fibres  were  named  after  the 
person  who  first  carefully  described  them,  and  called  the 
fibres  of  Sharpey.  The  firmness  of  the  matrix  is  due  to  the 
large  amount  of  mineral  matter  which  it  contains,  there 
being  about  sixty-five  per  cent,  of  inorganic  matter  in  bone. 
Of  these  inorganic  constituents  the  most  abundant  is  cal- 
cium phosphate.  In  small  quantities  there  occur  combina- 
tions of  fluorine,  chlorine  and  magnesia.  Small  quantities 
of  calcium  carbonate  are  present.  In  this  matrix  the  osteo- 
blasts are  not  merely  included  by  chance,  but  remain  there 
in  order  to  look  after  the  constant  wear  and  repair  of  the 
osseus  tissue.  By  extracting  the  proper  ingredients  from 
the  lymph  which  seeps  to  them,  they  are  enabled  wherever 
either  the  cell  itself  or  its  arms  touch,  to  secrete  new  bone, 


92 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


and  in  this  way  to  preclude  any  material  disintegration  of 
bone  in  any  part  of  the  body.  As  the  bone  substance  is 
everywhere  riddled,  even  to  the  smallest  bits,  with  these 
osteoblasts  and  their  ramifications  to  such  an  extent  that 


Fig.  43. — LAMELLAE  TORN  FROM  A  PARIETAL  BONE  TO  SHOW  THE  FIBRES  OF  SHARPEY, 
c,  c.     (After  Sharpey.) 
b,  thick  opaque  portion  of  bone,  a,  holes  where  fibres  had  been. 

the  point  of  an  ordinary  pin  would  really  cover  many  of 
them,  one  can  understand  under  what  thorough  supervision 
the  repair  of  normal  bone  is,  and  how  even  in  the  smallest 
and  most  out-of-the-way  portions  a  disintegration  or  soften- 
ing in  any  way  is  at  once  remedied.  The  osteoblasts  when 
once  included  in  these  lacunae  are  never  able  to  leave  them, 
but  remain  there  until  death  or  until  the  processes  of  age  in 
later  life  cause  many  of  them  to  apparently  disintegrate  and 
disappear.  This  disappearance  of  the  corpuscles  from  old 
bones,  as  well  as  the  continued  calcajeous  depositions  in  it, 
accounts  for  the  brittleness  of  the  bones  of  old  people  and 
the  difficulty  with  which  broken  portions  are  healed. 

The  Haversian  canal  with  its  series  of  lamellae,  lacunae 
and  canaliculi,  is  called  the  Haversian  system.  Where 
these  systems  meet,  irregular  bits  of  bone  frequently  fill  in 
the  space  between.  Around  the  outside  of  the  entire  bone 


THE    SUPPORTING   TISSUES.  93 

there  is  a  rather  strong  fibrous  membrane  completely  invest- 
ing it  except  at  the  ends,  called  the  periosteum.  This  is  a 
membrane  mostly  of  white  fibres  and  some  yellow  elastic 
tissue,  which  serves  to  carry  the  blood-vessels  which  are  to 
enter  and  nourish  the  bone.  In  the  meshes  of  this  perios- 
teum the  entering  blood-vessels  divide  and  branch,  and  so 
plunge  into  the  bone  at  many  different  points.  *  Immedi- 
ately under  the  periosteum  is  a  layer  of  ordinary  osteoblasts. 
The  connection  of  these  osteoblasts  with  the  formation  of 
bone  is  mentioned  further  on. 

The  current  notion  that  the  periosteum  is  the  thing  that 
nourishes  the  bone  and  even  produces  it  is  correct  only  in 
so  far  as  it  carries  and  distributes  the  blood-vessels  which 
enter  the  bone,  and  has  under  it  the  bone  corpuscles  which 
form  new  layers  of  bone.  For  this  reason,  if  in  any  surgical 
operation  or  otherwise  the  periosteum  is  removed  from  the 
bone,  the  bone  soon  dies  for  lack  of  nourishment.  The 
'ability  of  the  periosteum  with  the  osteoblasts  underneath  it 
to  form  bone  is  strikingly  illustrated  in  instances  where 
such  periosteum  removed  from  a  bone  was  tunneled  in 
among  muscles  and  in  that  position  gradually  developed  a 
new  bone.  But  it  must  be  remembered  that  this  formation 
of  new  bone  was  in  no  part  a  function  of  the  periosteum 
itself,  which  is  a  mere  connective  tissue  membrane,  nor 
even  of  the  blood-vessels  which  it  carries  in  numbers,  but 
of  the  osteoblasts  included  under  it. 

If  some  of  the  cancellated  bone  from  the  ends  be  exam- 
ined in  a  similar  way  under  a  microscope  as  the  section 
taken  from  a  shaft,  the  view  is  quite  similar,  except  that 
the  Haversian  systems  are  a  little  larger  and  their  arrange- 
ment not  so  compact. 

ORIGIN  AND  GROWTH  OF  BONE. 

In  the  way  in  which  bones  originate  in  the  body  they 
are  divided  into  two  classes,  called  the  membrane  bones 
and  the  cartilage  bones.  Membrane  bones  are  those  bones 
which  have  never  been  preceded  by  cartilage,  but  have 


94  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

developed  directly  from  a  membrane.  A  typical  example 
of  such  a  membrane  bone  is  the  parietal  bone  of  the 
skull. 

Growth  of  Cartilage  Bones. — Cartilage  bones  are  those 
bones  which  are  preceded  by  cartilage  which  has  been 
removed  and,  later,  bone  deposited  in  its  place,  or  as  com- 
monly stated  in  our  text-books,  bones  which  ossify  from 
cartilage.  If  the  limb  of  a  young  animal  be  examined  in 
embryonic  life  even  before  the  cartilages  have  made  their 
appearance,  the  following  series  of  changes  may  easily  be 
noticed: 

In  earliest  life  such  a  limb  budding  out  from  the  body 
would  consist  throughout  of  perfectly  similar  cells,  the 
original  descendants  of  the  primitive  egg  cell.  Soon  after, 
among  many  other  changes,  there  might  be  noticed,  in  the 
place  where  the  cartilage  is  to  appear,  to  form,  say  the 
humerus,  a  number  of  cells  similar  to  the  others  in  appear- 
ance, which,  however,  begin  to  secrete  between  themselves 
a  substance  familiar  to  us  as  cartilage.  In  this  cartilaginous 
matrix  these  cells,  which  we  may  now  call  cartilage  cells  or 
chondrioblasts,  multiply  and  by  a  continued  secretion  from 
these  the  matrix  of  the  cartilage  family  results.  As  this 
cartilage  is  plastic,  and  may  extend  by  interstitial  growth, 
it  soon  comes  to  possess  the  form  intended  for  the  future 
bone.  A  membrane  soon  invests  this  cartilage  except  at  the 
ends,  which  membrane  will  become  the  future  periosteum, 
which  now,  as  it  surrounds  cartilage,  is  called  the  peri- 
chondrium. 

This  membrane  becomes  filled  with  blood-vessels,  and 
underneath  it,  that  is  between  it  and  the  cartilage,  there 
come  to  lie  numerous  little  corpuscles,  the  osteoblasts  of 
the  future  bone.  At  this  stage  of  the  process  no  bone  is  yet 
present,  there  being  but  a  solid  cartilage  rod  of  the  form  of 
the  intended  humerus,  surrounded  by  the  membrane.  Soon 
after  this  the  process  commonly  called  the  process  of  ossi- 
fication begins. 


THE   SUPPORTING   TISSUES.  95 

This  is  generally  understood  to  mean  the  turning  of  the 
cartilage  into  bone,  but  such  a  change  in  no  sense  takes 
place.  Ossification  really  consists  in  the  gradual  removal 
of  the  cartilage  and  in  the  formation  of  entirely  new  bone. 
The  changes  which  convert  this  cartilage  into  the  bony 
humerus,  as  we  know  it,  are  as  follows:  * 

A  little  before  the  process  of  bone  formation  begins,  it 
may  be  noticed  that  the  cartilage  at  the  point  of  ossification 
becomes  somewhat  gritty,  probably  due  to  the  deposit  of 
extra  mineral  matter  in  the  cartilage.  In  the  case  of  the 
humerus  this  point  is  near  the  middle  of  the  shaft.  Soon 
after  this,  peculiar  large  cells  burrow  and  absorb  a  pas- 
sageway for  themselves  from  under  the  periosteum  through 
the  cartilage  until  they  reach  the  middle  of  the  shaft.  Here 
these  large  cells  continue  their  process  of  dissolving  and 
absorbing  the  cartilage,  and  so  tunneling  it  in  every  direc- 
tion. These  large  cells  are  called  osteoclasts,  or  possibly 
more  generally  myelo-plaques.  By  the  eating  away  of  the 
cartilage  in  this  way  the  central  portion  of  the  cartilagin- 
ous humerus  is  soon  converted  into  an  intricate  system  of 
tunnels,  which  gradually  extend  further  and  further  towards 
the  ends  of  the  bone.  The  absorption  of  the  cartilage  is 
probably  explained  as  due  to  the  digestive  action  of  the 
liquid  which  these  myelo-plaques  secrete.  What  happens  to 
the  cartilage  cells  themselves  when  their  matrix  is  removed 
is  not  yet  definitely  known.  According  to  some  observers  the 
cartilage  cells,  too,  are  absorbed;  while  according  to  other 
observers  these  cells  when  liberated  change  into  bone  cells, 
and  figure  in  a  way  to  be  described  later.  In  the  tunnels 
so  made,  blood-vessels  from  the  periosteum  grow,  and  from 
the  same  place  large  numbers  of  osteoblasts  follow  up  these 
channels.  These  osteoblasts  secrete  bits  of  bone  against 
the  walls  of  these  tunnels,  possibly  not  unlike  the  stone 
masonry  that  lines  many  railroad  tunnels.  When  finally  all 


*  As  the  changes  in  the  case  of  this  bone  are,  except  for  local  differences  the  same 
for  every  other,  this  one  instance  may  suffice  to  explain  the  phenomena  of  ossification 
wherever  occurring. 


96  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  cartilage  is  removed  and  nothing  but  this  mesh-work  of 
masonry  left,  there  is  produced  in  the  center  of  the  humerus 
what  is  familiar  to  us  as  spongy  bone.  Be  it  observed, 
however,  that  this  spongy  bone  is  in  no  sense  derived  from 
the  cartilage,  but  is  an  entirely  new  product,  and  that  all 
the  cartilage,  together  with  its  cartilage  cells,  has  been 
removed.  While  these  changes  are  going  on  in  the  shaft 
of  the  bone  the  osteoblasts  under  the  periosteum  have  begun 
to  secrete  bone  there,  and  so  have  surrounded  the  cartilag- 
inous shaft  with  a  fine  casing  of  osseous  tissue.  Layer 
after  layer  of  bony  lamellae  is  added  until  there  has  been 
formed  a  cylinder  of  bone  of  quite  appreciable  thickness, 
moulded  right  over  the  original  cartilage.  In  this  way  the 
new  bone  receives  at  once  the  shape  intended  for  it.  While 
the  strength  of  the  shaft  is  thus  added  to  under  the  peii- 
osteum,  new  osteoclasts,  or  myelo-plaques  begin  to  remove 
the  spongy  bone  just  deposited  where  the  cartilage  was 
removed.  In  this  way  by  the  continued  absorbing  action 
of  these  cells  there  is  soon  formed  an  empty  space,  the 
beginning  of  the  medullary  cavity.  The  tunneling  of  the 
cartilage  extends  further  and  further  towards  the  ends  of 
the  bone.  These  tunnels  are  then  immediately  lined  with 
layers  of  bone  by  succeeding  osteoblasts,  and  so  the  forma- 
tion of  spongy  bone  proceeds  gradually  towards  the  extrem- 
ities. This  spongy  bone  is,  however,  at  the  rear  end  being 
continually  absorbed  by  other  osteoclasts,  and  so  the  medul- 
lary cavity  reaches  further  and  further  towards  the  opposite 
ends.  If  this  continued  uninterrupted  and  with  the  rapidity 
with  which  it  goes  on  for  a  while,  it  would  soon  remove  all 
of  the  cartilage,  even  to  the  very  ends.  But  this  stage  is 
never  reached,  for  while  the  cartilage  is  being  continually 
encroached  upon  and  removed  at  one  end  it  keeps  elongat- 
ing above,  continuing  "to  do  so  until  the  full  length  of  the 
adult  bone  has  been  reached.  As  the  cartilages  at  the  ends 
grow  the  periosteum  creeps  further  and  further  along  it  and 
begins  the  deposition  of  bone.  In  this  way  the  bony  shaft 
follows  pari passu  the  enlargement  of  the  cartilage.  Thus 


THE   SUPPORTING   TISSUES.  97 

it  will  be  seen  that  bones  grow  in  length  really  by  the  car- 
tilaginous ends  growing,  and  then  the  cartilage  being 
removed  from  the  inner  side  in  the  manner  just  described. 

In  this  way  not  only  has  the  entire  cartilage  of  the  shaft 
been  removed,  but  as  the  periosteum  forms  more  and  more 
bone  beneath  itself  osteoclasts  begin  to  remove  bone  from 
the  medullary  cavity  side,  and  so  this  cavity  becomes  larger 
and  larger.  The  explanation  of  this  probably  consists  in 
the  fact  that  the  first  bone  deposited  by  the  periosteum  is 
not  as  strong  as  that  which  is  later  on  deposited,  and  so  it  is 
removed  in  order  to  avoid  surplus  weight.  This  eating 
away  of  the  bone  from  the  inner  side  continues  for  a  long 
time,  and  so  it  happens  that  the  medullary  cavity  of  an 
adult  bone  may  be  very  much  larger  than  the  piece  of  car- 
tilage which  originally  filled  it.  From  these  statements  it 
is  clear  that  the  bone  grows  in  thickness  only  by  the  addi- 
tion of  layers  around  the  outside  by  the  osteoblasts  under 
the  periosteum.  The  older  notion  that  a  bone  deposit  also 
takes  place  by  osteoblasts  which  line  the  medullary  cavity 
no  longer  seems  valid. 

The  encroachment  of  the  bone  into  the  cartilage  at  the 
end  does  not  reach  the  ends  of  the  bone  as  we  see  it  in  the 
adult  specimen,  but  after  the  cartilage  has  grown  to  the  size 
intended  for  the  future  bone,  independent  centers  of  ossifi- 
cation start  up  in  these  ends  with  processes  identical  with 
those  just  described.  In  this  way  the  bony  epiphyses,  as 
they  are  called,  at  the  ends  of  most  long  bones  arise.  L,ater 
on  the  cartilage  between  the  epiphyses  is  gradually  ab- 
sorbed from  both  sides  and  the  bone  becomes  continuous, 
or,  as  we  say,  the  bone  becomes  "knitted."  This  does  not 
take  place  until  quite  late.  For  instance,  in  the  humerus 
the  lower  epiphysis  unites  with  the  shaft  about  the  seven- 
teenth year;  the  upper  epiphysis  about  the  twentieth  year. 
In  the  femur  the  upper  end  is  joined  to  the  body  of  that 
bone  about  the  nineteenth  year,  and  the  lower  end  becomes 
knitted  about  the  twentieth  year.  In  the  fibula  this  knit- 
ting is  still  later,  occurring  at  the  lower  end  about  the 


98 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


twenty-first  year,  and  at  the  upper  end  about  the  twenty- 
fourth  year.     The  individual  vertebrae  which  fuse  together 


Fig.  44.— PART  OF  A  LONGITUDINAL  SECTION  OF  THE  DEVELOPING  FEMUR  OF  THE  RAB- 
BIT. DRAWN  UNDER  A  MAGNIFYING  POWER  OF  350  DIAMETERS.  (From  Klein  and 
Noble  Smith.) 

a,  rows  of  flattened  cartilage-cells;  b,  greatly  enlarged  cartilage-cells  close  to  the  ad- 
vancing bone,  the  matrix  between  is  partly  calcined;  c,  d,  already  formed  bone,  the  os- 
seous trabeculae  being  covered  with  osteoblasts  (<?),  except  here  and  there,  where  a  giant- 
cell  or  osteoclast  (/),  is  seen,  eroding  parts  of  the  trabeculae;  g,  h,  cartilage-cells  which 
have  become  shrunken  and  irregular  in  shape.  From  the  middle  of  the  figure  downwards 
the  dark  trabeculae,  which  are  formed  of  calcined  cartilage  matrix,  are  becoming  covered 
with  secondary  osseovis  substance  deposited  by  the  osteoblasts.  The  vascular  loops  at 
the  extreme  limit  of  the  bone  are  well  shown,  as  well  as  the  abrupt  disappcarmu-c  of  the 
cartilage-cells. 

to  form  the  sacrum,  and  which  are  ossified  from  five  differ- 
ent centers,  unite  as  late  as  the  twenty-fifth  year,  while  the 


THE    SUPPORTING   TISSUES.  99 

three  bones  that  form  the- os  innominatum,  unite  about  the 
same  time.  Thus  we  may  see  that  the  human  body  does 
not  reach  its  skeletal  maturity  until  about  twenty-five  years 
of  age.  From  a  hygienic  standpoint  this  ought  not  to  be 
forgotten,  for  loads  that  a  man  of  thirty  may  carry  without 
the  least  danger,  may  prove  disastrous  for  a  lad  of  eighteen 
or  nineteen,  in  spite  of  the  strength  of  his  muscles. 

Some  interesting  experiments  have  been  made  in  order 
to  determine  the  manner  of  growth  of  bones,  by  feeding 
young  pigs  madder.  In  this  madder  there  seems  to  be  a 
compound  which  colors  bone  in  which  it  is  deposited  red. 
When,  now,  such  a  pig  in  question  has  for  a  month  or  two 
been  fed  with  madder,  and  is  then  killed  and  the  bone 
examined,  it  is  found  that  there  is  a  layer  of  reddish  bone 
immediately  under  the  periosteum  and  zones  at  the  ends 
where  the  cartilage  has  been  encroached  upon.  All  the 
bone,  however,  next  to  the  medullary  cavity  remains  un- 
stained. By  taking  such  a  pig  and  feeding  it  this  madder, 
in  alternate  months,  it  is  possible  to  produce  characteristic 
rings  of  red  and  white,  encircling  the  shaft  of  the  bone 
under  the  periosteum  and  zones  of  red  and  white  alternat- 
ing at  the  extremities.  That  the  shaft  itself  does  not  grow 
is  easily  demonstrated  by  driving  some  pointed  pegs  into 
the  shaft  of  a  living  bone,  and  then  measuring  their  relative 
distances  after  a  certain  period  has  elapsed.  In  the  shaft 
of  the  bone  these  pegs  do  not  separate,  showing  that  no 
elongation  has  taken  place.  If,  however,  one  of  the  pegs 
be  inserted  in  the  cartilaginous  end  the  regular  elongation 
appears. 

The  bone  which  is  deposited  under  the  periosteum  is 
deposited  in  successive  layers,  much  like  the  layers  of  an 
onion.  These  layers  of  lamellae  do  not  show  the  character- 
istic arrangement  of  the  Haversian  systems,  as  described 
on  a  former  page.  To  explain  how  these  circumferential 
lamellae  become  later  changed  into  the  characteristic  Haver- 
sian systems  is  at  present  no  easy  matter,  but  it  is  believed 
on  good  grounds  that  the  circumferential  lamellae  are  actu- 


100  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

ally  removed  piecemeal,  and  replaced  by  a  new  growth  of 
bone  extending  into  it  from  beneath.  To  state  it  again,  it 
is  probably  the  migration  of  the  Haversian  systems  of  the 
deeper  portions  of  the  bone  into  the  outer  layers,  accomr 
plished  no  doubt  by  a  piecemeal  absorption  of  these  outer 
layers  and  the  re-deposition  of  new  bone,  showing  the 
Haversian  system.  It  is  possible  that  this  change  from  the 
stratified  appearance  of  the  layers  under  the  periosteum  to 
the  normal  Haversian  systems  is  to  be  accounted  for  on  the 
grounds  that  the  latter  system  is  better  adapted  for  the 
nourishment  of  the  bone,  and  that  possibly  for  physical 
reasons  the  columnar  arrangement  of  the  Haversian  systems 
is  stronger  than  that  of  the  stratified  lamellae.  Future 
investigation,  however,  must  solve  for  us  a  number  of  ques- 
tions still  unanswered  in  this  matter. 

While  the  bones  do  not  grow,  as  we  ordinarily  use  that 
term,  after  the  twenty-fifth  year,  they  may  change  their 
shapes  to  some  extent ;  for  throughout  the  greater  part  of 
life  there  is  an  absorption  of  bone  in  some  places  where  it  is 
no  longer  needed,  and  a  continued  deposition  in  other  places 
where  added  strength  is  desired.  When  bones  are  mechan- 
ically broken  they  are  united  by  having  osteoclasts  first 
remove  the  dead  bone  from  the  broken  ends,  and  then  hav- 
ing the  osteoblasts  cement  the  pieces  together  with  new 
bone,  which  may  in  some  cases  even  be  preceded  by  a 
formation  of  cartilage.  This  removal  of  the  dead  bone  is 
probably  identical  in  process  with  the  removal  of  the  car- 
tilage and  bone  regularly  occurring  in  their  growth. 

Such  bone  absorption  occurs  in  the  milk  dentation  and 
also  explains  the  occasional  loosening  of  the  permanent  set 
of  teeth,  owing  to  the  removal  of  the  cement,  which  is  really 
bone. 

While  in  the  long  bones  there  is  usually  a  single  center 
of  ossification,  near  the  middle  of  the  shaft,  with  later  ones 
to  form  the  epiphyses,  they  may  be  much  more  numerous 
in  irregular  bones.  Thus  in  the  irregular  sphenoid  bone 


THE    SUPPORTING    TISSUES. 


101 


there  are  as  many  as  eight  different  points   at  which  the 
process  of  ossification  begins. 

Growth  of  Membrane  Bones. — The  second  class  of  bones 
comprises  the  membrane  bones.  As  previously  stated,  these 
are  bones  which  are  never  preceded  by  cartilage.  A  typi- 
cal illustration  of  such  a  membrane  bone  is  the  parietal. 
Preceding  this  bone  in  early  life  there  is  just  an  ordinary 
connective  tissue  membrane,  containing  no  mineral  deposit 


Fig.  45.— PART  OF  THE  DEVELOPING  PARIETAL  BONE  OF  A  FOETAL  CAT.  (After  Schafer.) 
sp,  bony  spicules,  with  some  of  the  osteoblasts  imbedded  in  them,  producing  the 
lacunae;  ost,  osteoblasts  partly  imbedded  in  the  newly  formed  bone;  of,  osteogenic  fibres 
prolonging  the  spicules,  with  osteoblasts  between  them  and  applied  to  them;  a,  granules 
of  calcareous  deposit  between  the  osteogenic  fibres;  at  b  the  granules  have  become 
blended,  and  the  matrix  is  clearer;  at  c  a  continuity  is  established  between  the  two  adja- 
cent spicules. 

of  any  kind.  Portions  of  this  membrane  are  still  evident 
on  the  skull  of  a  new-born  child,  and  are  familiar  as  the 
fontannelles.  In  the  meshes  of  this  membrane  osteoblasts 
find  their  way,  which  begin  at  once  to  secrete  over  it  the 
mineral  matter  of  the  bone.  By  this  continued  secretion  of 


102  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

bone  in  and  around  this  membrane  the  fully  formed  parietal 
comes  to  be.  While  not  strictly  analagous,  the  primitive 
membrane  might  be  compared  with  the  periosteum,  next  to 
which,  as  in  the  long  bone,  occurs  the  mineral  deposit. 

CHEMICAL  COMPOSITION  OF  BONE. 

The  chemical  composition  of  bone  has  been  referred  to. 
Human  bone  consists  of  sixty-five  per  cent,  inorganic  mat- 
ter and  thirty- five  per  cent,  organic  matter.  This  organic 
matter  consists  of  a  matrix  called  osseine,  with  which  the 
inorganic  constituents  so  combine  that  even  under  a  micro- 
scope it  looks  homogeneous.  This  osseine  is  easily  changed 
by  boiling  it,  into  the  familiar  gelatine.  In  fact,  much  of 
the  gelatine  of  commerce  is  derived  from  the  bones  of 
slaughtered  animals,  and  an  integral  ingredient  of  the  soup 
made  by  boiling  a  soup  bone  is  gelatine.  It  figures  further 
in  a  variety  of  roles  in  the  preparation  of  foods  and  desserts 
familiar  to  every  household  cook.  The  mineral  salts  are 
mainly  calcium  phosphate  and  calcium  carbonate,  and  from 
this  mineral  part  of  bone-earth  much  of  the  phosphorus  of 
commerce  is  derived.  By  placing  a  bone  in  weak  hydro- 
chloric acid  it  is  possible  to  dissolve  out  the  mineral  salts 
and  leave  nothing  but  the  organic  portions.  Such  a  bone 
is  soft  and  flexible.  On  the  other  hand,  it  is  possible  to  re- 
move the  organic  portion  by  what  is  known  as  calcining  the 
bone  in  a  hot  fire,  which  burns  up  all  the  organic  matter. 
In  this  way  the  bone-dust  of  commerce  is  made.  When 
the  organic  matter  of  a  bone  is  not  completely  burned  up, 
but  charred,  it  forms  the  familiar  bone-black  used  in  many 
ways  in  the  arts  and  in  commerce,  especially  in  the  purifi- 
cation of  sugar. 

HISTORICAL. 

As  early  as  1736  Nesbitt  showed  that  some  flat  bones 
were  formed  perfectly  independently  of  cartilage,  and  even 
insisted  that  the  cartilage  was  often  destroyed  in  cases 
where  it  did  precede  the  real  bone  structure.  The  primi- 


THE   SUPPORTING  TISSUES. 


103 


live  cartilage  he  explained  as  a  mere  temporary  substitute 
used  to  mould  the  shape  of  the  succeeding  bone,  but  as  he 
was  unable  to  actually  demonstrate  his  views  as  they  are 
now  demonstrated  with  the  microscope,  they  were  but  little 
credited  until  Sharpey,  in  1846,  made  clear  beyond  all  ques- 
tion the  manner  of  the  formation  of  bone  and  the  replace- 
ment of  the  cartilage. 

Cartilages. 

The  second  kind  of  the  supporting  tissues  comprises 
the  cartilages,  familiar  under  the  more  common  name  of 
gristle.  Cartilage  differs  from  bone  in  the  fact  that  the 
cells  which  fill  it  are  not  branched,  but  smooth,  and  the 
matrix  does  not  possess  a  system  of  canals  and  canaliculi. 
As  a  rule  the  mineral  ingredients  are  much  less  in  propor- 
tion than  in  bone,  although  in  older  cartilages  a  calcifica- 
tion takes  place  which  results  in  giving  to  the  cartilage  as 


Fig.  46.— HYALINE  CARTILAGE  FROM  THE  LOWER  END  OF  TIBIA.    (After  Schafer.) 
«,  6,  c,  different  arrangement  of  cell  groups ;  d,  layer  of  calcified  cartilage ;  e,  bone. 

great  a  proportion  of  earthy  matter  as  bone  possesses. 
But  such  calcified  cartilage  is  structurally  entirely  different 
from  bone. 


104 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


Three  fairly  distinct  types  of  cartilage  occur,  the  hya- 
line, the  yellow  elastic  and  the  white  fibrous.  In  the  hya- 
line cartilage,  as  the  name  suggests,  the  matrix  seems  en- 
tirely homogeneous ;  that  is,  devoid  of  any  fibrillation.  In 
this  structureless  material  the  cartilage  cells  are  imbedded. 
A  view  held  by  some  histologists  that  this  apparently  struc- 
tureless matrix  is  permeated  by  a  system  of  very  fine  canals , 
lacks  verification.  Such  hyaline  cartilage  is  found  regularly 
at  the  ends  of  bones,  where  a  smooth,  articulating  surface 
is  necessary.  The  yellow  elastic  cartilage  differs  from  hya- 
line in  having  the  matrix  made  up  of  densely  packed  yellow 
elastic  fibres,  in  the  close  meshes  of  which  the  cartilage 
cells  are  lodged.  Such  cartilage  occurs  in  the  ear  and  the 


Fig.   47.— YELLOW    ELASTIC    CONNECTIVE 
TISSUE  FIBRES.     (After  Sharpey.) 


Fig.   48.— YELLOW     ELASTIC     CARTILAGE 

FROM    THE    EAR. 


tip  of  the  nose,  and  is  peculiarly  well  adapted  to  admit 
slight  alterations  in  position  or  form.  The  white  fibrous 
cartilage,  as  the  name  suggests,  is  composed  of  a  matrix  of 
closely  pressed  white  fibres,  with  the  contained  cartilage 
cells  packed  between  them.  Such  cartilage  is  found  in 
many  places  as  disks  between  articulating  bones ;  it  binds 
together  contiguous  bones  forming  connecting  fibres  between 


THE   SUPPORTING  TISSUES. 


105 


them,  and  in  still  other  cases  it  lines  bony  grooves  in  which 
tendons  of  muscles  glide.     Such  cartilage  is  pre-eminently 


'*HJ 

Fig.  49.— WHITE  FIBROUS  CARTILAGE  FROM  AN  INTERVERTEBRAL  DISK.   (After  Schafer.) 

fitted  for  positions  where  strength  and  rigidity  are  required. 
The  cartilages  shade  off  insensibly  and  without  any  sharp 
line  of  demarkation  into  the  connective  tissues  proper,  that 


Fig.  50. — TRANSITION  FROM  CARTILAGE. 
a,  through  the  intermediate  form  b,  to  connective  tissue,  6,  on  the  right. 

tissue  which  pervades  all  the  organs  of  the  body  and  is  the 
framework  of  every  structure. 

Connective  Tissues  Proper. 

Of  these  connective  tissues  proper,  two  varieties  occur. 
The  elastic  is  composed  of  thick,  wavy,  yellow  elastic  threads, 
which  frequently  branch.  This  tissue  is  found  in  those  parts 
of  the  body  where  elasticity  is  desirable,  as  for  instance,  in 
the  walls  of  the  arteries  and  veins,  and  is  to  a  large  extent 
the  prevailing  tissue  in  the  lung.  The  white  fibrous  tissue, 
on  the  other  hand,  is  composed  of  bundles  of  smaller, 
straighter  white  threads  possessing  little  or  no  elasticity. 
This  tissue  is  especially  well  exhibited  in  the  tendons  and 


106 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


gives  to  these  their  strength.  As  far  as  the  fibres  are  con- 
cerned, there  is  but  little  difference  between  the  yellow 
elastic  and  the  ^  white  fibres -of  cartilage,  and  the  corre- 


Fig.  51.— CONNECTIVE  TISSUE  CORPUSCLES.    (After  Schafer.) 

sponding  ones  of  connective  tissue,  their  classification  into 
cartilage  or  connective  tissue  being  determined  rather  by 
the  closeness  of  these  threads  and  the  shape  of  the  cor- 
puscles which  are  included.  In  the  cartilages,  on  account 


Fig.  52.— FIBRES  OF  AREOLAR  TISSUE. 


of  the  firm  texture,  the  cells  are  round  and  have  little  lati- 
tude   to  move   about.     In    the  connective  tissues,   on   the 


THE    SUPPORTING   TISSUES.  107 

other  hand,  the  meshes  being  much  more  open,  the  enclosed 
cells  become  much  branched  and  have  the  power  to  move 
about.  Such  wandering  connective  tissue  corpuscles  are 
not  always  easily  distinguished  from  wandering  blood  cor- 
puscles. While  in  the  case  of  cartilage  the  yellow  elastic 
varieties  and  the  white  fibrous  varieties  are  found  tolerably 
separate,  in  the  connective  tissues  we  frequently  find  both 
making  up  the  framework  of  the  structure  in  question. 
Such  a  mixture  of  yellow  elastic  and  white  fibrous  tissue  is 
called  areolar  tissue,  and  is  particularly  well  exemplified  in 
the  connective  tissue  under  the  skin. 

Humors. 

A  final  kind  of  supporting  tissues  frequently  classed  with 
the  connective  tissues  proper  are  the  humors  of  the  eye.  In 
these  the  matrix  has  never  become  hard  with  mineral  de- 
positions, has  never  developed  fibres  in  it  of  any  kind,  but 
remains  almost  perfectly  liquid.  The  connective  tissue 
cells  which  have  formed  these  humors,  later  on  atrophy  and 
practically  disappear,  leaving  this  structureless  matrix 
behind. 

FORMATION  OF  CARTILAGE  AND  CONNECTIVE  TISSUE. 

In  their  manner  of  formation  all  the  supporting  tissues 
are  alike.  They  are  not  made  by  a  direct  differentia- 
tion of  cells  into  these  tissues,  but,  as  stated  once  before, 
are  formed  as  a  secondary  product  by  the  cells.  In  the 
case  of  bone,  this  deposition  has  been  treated  at  length.  In 
the  remaining  supporting  tissues  the  origin  is  quite  similar, 
save  that  the  cartilages  and  connective  tissues  are  not  added 
continually  from  the  outside,  but  grow  throughout  the  en- 
tire substance;  that  is,  it  is  a  growth  by  intussusception. 
The  cartilage  cells  in  the  matrix  retain  the  power  to  divide, 
and  new  cells  formed  by  such  division  separate  by  the 
secretion  of  more  matrix  between  them.  In  the  case  of  the 
yellow  elastic  cartilage  this  has  been  specially  worked  out. 
Here  the  matrix  is  first  deposited  in  the  form  of  little 


108  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

granules,  probably  secreted  or  excreted  by  the  cartilage 
cells,  which  granules  later  on  in  some  way  not  yet  under- 
stood, fuse,  forming  the  characteristic  fibres.  While  most 
cartilages  have  a  membrane  around  them  called  the  peri- 
chondrium,  such  a  membrane  does  not  figure  in  any  way  as 
it  does  in  the  formation  of  bone,  but  is  here  merely  an  en- 
veloping membrane  supplied,  of  course,  with  blood-vessels. 


Fig.  53.— DEVELOPMENT  OF  ELASTIC  TISSUE  BY  THE  DEPOSITION  OF  ROWS  OF  ELASTIC 

GRANULES,  0,  FINALLY  FUSING  INTO  A  PLATE-LIKE  EXPANSION  OF  ELASTIC  SUBSTANCE 

INDICATED  AT  P.     (After  Ranvier.) 

The  method  of  origin  of  yellow  elastic  tissue  just  cited, 
probably  does  not  differ  from  the  manner  in  which  the  con 
nective  tissues  proper  and  the  humors  arise,  save  that  in 
these  the  corpuscles  which  have  produced  them  may  actu- 
ally wander  out  and  leave  nothing  but  their  product  behind. 
The  supporting  tissues  being  thus  not  directly  composed  of 
cells,  possess  no  physiological  activity,  and  when  once 
formed  probably  remain  entirely  unaltered  during  life.  The 
various  forms  do  not  differ  much  in  chemical  composition, 
except  the  yellow  elastic,  all  yielding  when  boiled,  a  variety 
of  gelatine.  Their  similar  nature  is  further  indicated  in  the 
fact  that  they  replace  each  other  easily.  Thus,  cartilages 
are  replaced  by  bone,  and  broken  bones  are  sometimes 
cemented  together  by  the  formation  of  cartilage. 

HYGIENE  OF  SUPPORTING  TISSUES. 

In  reference  to    the    supporting   tissues,  little  need  be 
said  from  the  standpoint  of  their  hygiene.     It  is,  of  course, 


THE    SUPPORTING   TISSUES.  109 

apparent  that  in  young  persons  the  food  should  contain  suf- 
ficient amounts  of  mineral  salts,  otherwise  the  bones  will 
not  acquire  their  intended  hardness.  Milk  is  peculiarly 
adapted  for  this,  containing  quite  a  large  amount  of  earthy 
matter.  It  not  infrequently  happens  that  children,  in 
spite  of  an  apparently  rich  diet,  are  really  starving  for 
want  of  the  mineral  matters  which  are  needed  to  give  con- 
sistency to  these  supporting  tissues.  The  final  hygienic 
recommendation  that  no  unusual  strains  of  any  kind  shall 
be  placed  upon  any  of  them  while  they  are  in  their  forma- 
tive period,  is  too  plain  to  need  further  comment. 

JOINTS. 

The  supporting  tissues  not  only  serve  to  give  form  and 
outline  to  the  body,  but  in  the  case  of  bones  they  serve  to 
make  a  system  of  levers  to  accomplish  the  various  move- 
ments of  which  the  body  is  capable.  To  permit  such  move- 
ments, bones  are  articulated  together  to  form  more  or  less 
movable  joints.  In  the  body  there  are  found  four  kinds  of 
movable  joints.  They  are,  first,  the  gliding  joints;  second, 
the  pivot  joints;  third,  the  hinge  joints,  and  fourth,  the 
ball-and-socket  joints.  In  addition  to  these  movable  joints, 
bones  articulate  in  such  a  way  as  to  preclude  motion.  In- 
stances of  such  articulation  are  plain  in  the  bones  of  the 
skull,  where  the  bones  remain  separate  until  the  skull  has 
reached  its  mature  size.  Such  articulations  are  called 
sutures. 

In  the  gliding  joints  a  number  of  bones  glide  over  each 
other  to  such  an  extent  as  to  permit  quite  a  little  motion. 
Instances  of  such  joints  are  in  the  wrists. and  ankles.  Here 
the  carpal  and  tarsal  bones  gliding  over  each  other  permit 
all  the  different  motions  of  which  the  wrist  and  ankle  are 
possible.  There  are  but  two  instances  of  pivot  joints  in  the 
body.  The  plainest  instance  is  the  joint  between  the  atlas 
and  the  axis,  where  the  odontoid  process  of  the  axis  forms 
the  pivot,  around  which  the  atlas  rotates.  A  second  illus- 
tration is  in  the  case  of  the  forearm,  where,  by  the  peculiar 


110  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

gliding  motion  of  the  radius  at  the  elbow,  the  hand  may  be 
pronated  and  supinated  by  having  the  radius  turn  on  the 
ulna  as  a  pivot.  The  hinge  joints  occur  in  greater  num- 
ber, being  found  in  the  elbow,  the  knee,  and  in  the  phal- 


Fig.  54.— ARTICULATIONS  OF  THE  PELVIS  AND  HIP-JOINT,   SEEN  FROM  BEFORE.     THE 

ANTERIOR    HALF    OF    THE    CAPSULAR    LIGAMENT    OF  THE   LEFT   HIP-JOINT   HAS   BEEN 
REMOVED,  AND  THE  FEMUR  ROTATED  OUTWARDS.      (Allen  Thomson.) 

1,  anterior  common  ligament  of  the  vertebrae  passing  down  to  the  front  of  the 
sacrum;  2,  ilio-lurnbar  ligament;  3,  anterior  sacro-iliac  ligament;  4,  placed  in  the  great 
sacro-sciatic  foramen,  points  to  the  small  sacro-sciatic  ligament;  5,  a  portion  of  the  great 
sacro-sciatic  ligament;  6,  anterior  ligament  of  the  symphysis  pubis;  7,  obturator  mem- 
brane; 8,  capsular  ligament  of  hip-joint;  the  figure  is  placed  on  its  ilio- femoral  band;  9, 
upper  part  of  the  divided  capsular  ligament  of  the  left  hip-joint  near  the  place  of  its  at- 
tachment to  the  border  of  the  acetabulum ;  10,  placed  on  the  os  pubis  of  the  left  side  above 
the  transverse  ligament  of  the  acetabular  notch.  The  head  of  the  femur  is  withdrawn 
partially  from  the  socket,  so  as  to  show  the  iuterarticular  ligament  stretched  from  the 
transverse  ligament. 

anges  of  hand  and  foot.  The  joint  which  seems  capable  of 
giving  the  greatest  latitude  of  motion,  is  the  ball-and- 
socket  joint,  examples  of  which  are  the  joints  at  the  shoul- 
der and  at  the  hip. 

In  order  to  make  these  articulating  surfaces  as  smooth 
as  possible,  bits  of  cartilage  cover  the  ends  of  the  bones. 
These  are  covered  next  to  the  joint  by  a  delicate  membrane 


THE   SUPPORTING   TISSUES. 


Ill 


called  the  synovial  membrane,  which  secretes  a  fluid  known 
as  the  synovial  fluid,  intended  probably  as  a  kind  of  lubri- 
cant to  reduce  the  friction  to  a  minimum.  To  make  these 


Fig.  55.  Fig.  56. 

Fig.  55.— RIGHT  KNEE-JOINT,  FROM  THE  INNER  SIDE  AND  ANTERIORLY.  (Allen  Thomson.) 
1,  tendon  of  the  rectus  muscle  near  its  insertion  into  the  patella;  2,  insertion  of 
the  vastus  internus  into  the  rectus  tendon  and  side  of  the  patella;  3,  ligamentum  patel- 
lae descending  to  the  tubercle  of  the  tibia;  4,  capsular  fibres  forming  a  lateral  ligament 
of  the  patella  prolonged  in  part  from  the  insertion  of  the  vastus  internus  downwards 
towards  the  inner  tuberosity  of  the  tibia;  5,  internal  lateral  ligament;  6,  tendon  of  the 
semimembranosus  muscle. 

Fig.  56.— THE  LIGAMENTS  OF  THE  WRIST  JOINT,  DORSAL  VIEW. 

joints  firm  and  preclude  the  possibility  of  displacement, 
they  are  wrapped  with  a  series  of  ligaments  extending 
from  one  bone  to  the  other,  so  as  to  make  impossible  the 
relative  displacement  of  the  articulating  surfaces. 


CHAPTER  VII. 


MUSCLES  AND  PHENOMENA  OF  CONTRACTION. 

Probably  the  most  striking  characteristic  of  any  living 
body  is  its  ability  to  move.  But  this  power  of  motion  is  by 
no  means  a  property  of  all  living  things.  The  entire  realm 
of  plants,  with  exceptions  of  course  which  need  not  concern 
us  here,  is  devoid  of  the  power  of  actual  movement,  and 
there  are  some  animals  whose  ability  to  move  from  place  to 
place  is  entirely  wanting.  The  movements  of  our  bodies 
are  caused  by  the  contraction  of  organs  familiar  to  every 
one  as  the  muscles.  There  are,  however,  in  the  body  struc- 
tures other  than  the  muscles  which  possess  this  power  to  a 
certain  extent.  Thus,  many  of  the  varieties  of  white  cor- 
puscles, such  as  the  white  blood  corpuscles,  cartilage  cells, 
connective  tissue  cells,  are  able  to  move  from  place  to 
place.  Such  locomotion  is  described  as  amoeboid.  The 
power  of  active  movement  also  occurs  in  ciliated  cells 
which  are  found  lining  the  entire  respiratory  system,  with 
the  exception  of  the  pharynx  and  the  internal  lung  cells, 
and  which  occur  also  in  the  internal  genital  ducts.  Such 
cells  consist  of  a  main  body  which  shows  no  power  of 
motion,  but  is  continued  at  one  end  into  a  number  of 
thread-like  prolongations,  which  have  the  power  of  moving 
rapidly  backwards  and  forwards.  The  expulsion  of  the 
phlegm  from  the  respiratory  passages  up  into  the  mouth  is 
accomplished  by  such  ciliated  action.  It  is  interesting  to 
observe  that  all  the  cilia  of  a  membrane  seem  to  move  in 
harmony,  the  movements  of  the  cilia  sweeping  across  the 
surface  like  waves  of  moving  grain  through  a  wind-swept 
wheat  field.  In  the  internal  genital  ducts  they  serve  to 
(112) 


MUSCLES   AND   PHENOMENA   OF   CONTRACTION.          113 

propel  the  re-productive  elements.  The  real  organs  of 
movement  are,  however,  the  muscles.  A  careful  examina- 
tion of  the  entire  muscular  system  of  the  body  shows  at 
once  three  tolerably  distinct  kinds  of  muscles.  First,  the 
voluntary  or  skeletal  muscles ;  or,  on  account  of  their  mi- 
croscopic appearance  to  be  described  later,  cross-striated 
muscles.  Second,  the  involuntary,  visceral  or  plain  muscles. 
Third,  the  muscles  which  form  the  heart,  and  which  differ 
materially  from  both  of  the  preceding,  and  occupy  from 
an  anatomical  point  of  view  an  intermediate  position. 

Voluntary  Muscles. 

As  the  name  indicates,  these  muscles  are  under  the  con- 
trol of  the  will.  This  is,  however,  not  absolutely  true,  as 
there  are  a  number  of  muscles  over  which  the  control  of  the 
will  has  been  lost.  Thus,  there  are  some  muscles  of  the  ear 
which,  if  they  could  be  used,  would  serve  to  move  that 
organ,  but  the  power  to  move  them  has  been  entirely  lost. 
That  nearly  all  of  these  muscles  are  attached  to  bones  has 
given  them  the  name  of  skeletal  muscles.  But  there  are 
exceptions  to  this  as  well.  Thus  the  circular  mucles  enclos- 
ing the  mouth  or  the  eyes,  are  not  attached  at  all  to  any 
bone,  and  yet  are  voluntary  in  the  highest  degree.  The 
real  classification  is  based  upon  their  minute  structure,  and 
in  this  all  agree  in  showing  under  the  high  power  of  the 
microscope  peculiar  cross  striations  to  be  discussed  later. 

TYPES  OF  VOLUNTARY  MUSCLES. 

A  typical  muscle  is  composed  of  a  thick,  central  portion 
called  the  belly,  which  tapers  at  each  end  into  a  thick 
string  of  white  fibrous  tissue  familiar  as  the  tendon.  From 
this  type,  however,  there  are  many  deviations.  Thus  the 
muscle  which  serves  to  bend  the  arm  forward,  ends  at  the 
shoulder  in  two  tendons  instead  of  one.  This  has  given 
the  name  of  biceps  to  this  muscle.  Immediately  under  the 


114 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


arm  lies  the  muscle 


Fig.   57. —  SHOWING    THE 

SUPERFICIAL  MUSCLES 
OF  THE  RIGHT  ARM, 
FROM  BEFORE. 

1,  l',  pectoralis  major; 
2,  2',  deltoid;  3,  3',  3", 
biceps;  4,  4',  brachialis 
auticus;  5,  5',  triceps. 
Numbers  from  6-17  refer 
to  muscles  and  tendons  of 
fore-arm  and  hand. 


which  serves  to  extend  the  arm,  which 
ends  in  three  tendons  at  the  shoulder, 
and  is  called  the  triceps.  Then  again 
there  are  muscles  which  have  a  tendon 
in  the  middle,  thus  dividing  the  muscle 
into  two  portions.  Such  a  muscle  is 
called  a  digastric  muscle,  that  is,  has 
two  bellies.  Sometimes  even  more  than 
two  occur,  when  the  muscle  is  called  a 
polygastric  muscle.  Instances  of  such 
polygastric  muscles  are  found  in  the 
anterior  abdominal  wall.  Closer  exam- 
ination of  a  typical  muscle  will  show 
it  divided  up  into  bundles  separated 
from  each  other  by  intervening  con- 
nective tissue.  On  a  cross  section  of 
a  muscle  these  bundles  would  appear 
as  irregular  areas,  and  are  familiar  to 
every  one  in  the  characteristic  appear- 
ance of  a  piece  of  lean  beefsteak.  This 
connective  tissue  not  only  extends 
through  the  muscle,  dividing  it  up  into 
bundles  which  are  called  fasciculi,  but 
envelopes  the  entire  muscle.  It  serves 
to  carry  the  nerves  and  blood-vessels 
through  the  muscle,  and  is  called  the 
perimysium. 


HISTOLOGY  OF  VOLUNTARY  FIBRES. 

Fibrillation. — For  a  more  detailed  study  the  microscope 
must  be  called  to  aid,  and  it  is  then  seen  that  the  fasciculi 
are  divided  into  still  smaller  bundles,  and  that  the  smaller 
bundles  are  finally  composed  of  the  ultimate  fibres.  These 
muscle  fibres  all  run  in  the  same  direction,  which  accounts 
for  the  splitting  observed  on  any  piece  of  boiled  beef.  If 


MUSCLES   AND    PHENOMENA    OF   CONTRACTION.         115 

such  a  small  bundle  be  teased  under  the  microscope  into  its 


Fig.  58.— SEVERAL  VOLUNTARY  MUSCLE  FIBRES.    (After  Sharpey.) 
a,  end  view  of  fasciculus ;  6,  6,  individual  fibres ;  c,  a  fibre  splitting:  into  longitudinal 
fibrils. 

ultimate  fibres,  the  following  points  may  be  noticed  con- 
cerning their  finer  structure: 

Striation. — The  fibres  appear  cross-striped.    This  is  not 
due,  however,   to   markings  running   on  the  outside  of    a 


Fig.  59.— PORTION  OF  A  HUMAN  MUSCULAR 

FIBRE  SHOWING  THE  ALTERNATE  LIGHT 
AND  DARK  BANDS,  AND  IN  THE  LIGHT 
r.A.XI)  THE  MK.M15RANE  OF  KRAUSE. 

(After  Sharpey.) 


Fig.  60. — Two  VOLUNTARY  FIBRES.     (After 

Gegenbaur.) 

n,   nuclei    under    sarcolemma ;    s,   sar. 
colemma  visible  where  the  fibre  is  torn. 


muscle,  but  it  is  due  to  the  fact  that  a  muscle  fibre  is  com- 


116  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

posed  of  alternating  light  and  dark  disks,  somewhat  like  a 
stack  of  coin  might  be  composed  of  alternate  copper  cents 
and  silver  dimes.  If  a  crushed  portion  of  a  fibre  be  exam- 
ined it  is  possible  to  make  out  a  delicate  covering  extend- 
ing entirely  around  the  fibre,  known  as  the  sarcolemma.  In 
this  sarcolemma  lie  the  more  or  less  semi-liquid  contents, 
which  exhibit  the  striation  referred  to. 

Nuclei. — Scattered  along  the  fibre  here  and  there,  and 
lying  immediately  underneath  the  sarcolemma,  are  nuclei. 

Measurements  of  an  Individital  Fibre. — Measurements 
of  these  fibres  in  an  adult  muscle  give  a  length  of  from  one- 
half  inch  to  an  inch  and  a  half,  and  a  width  of  about  one 
five-hundredth  of  an  inch.  L,ittle  floating  gossamer  threads 
cut  in  lengths  of  an  inch  or  more  may  serve  to  give  us  an 
idea  of  their  actual  size.  It  will  be  seen  from  their  length 
that  an  individual  muscle  fibre  does  not  run  the  entire 
length  of  a  muscle,  as  many  muscles  are  five,  six,  or  more 
inches  in  length. 

Attachment  to  Tendons. — A  delicate  fibril  from  the  ten- 
don may  be  traced  to  the  end  of  a  muscle  fibre  where  it  is 
directly  cemented  to  the  sarcolemma.  An  older  view  that 
the  tendons  are  but  the  connective  tissue  of  a  muscle 
extended,  is  no  longer  tenable.  Whether  such  tendon 
fibrils  run  to  both  ends  of  all  fibres,  is  still  a  matter  of 
question.  Some  histologists  claim  two  or  more  muscle  fibres 
may  be  cemented  end  to  end;  others  again  that  the  muscle 
fibres  are  twisted  and  intertwined  with  each  other  some- 
what like  threads  in  a  rope,  and  that  tendons  attach  them- 
selves merely  to  the  outermost  fibres.  The  probability  of 
the  matter,  however,  is  that  in  the  majority  if  not  in  all 
cases  each  individual  fibre  receives  at  both  of  its  ends  a 
delicate  little  fibril  from  the  tendon,  which  fibril  is  directly 
and  firmly  cemented  to  its  sarcolemma.  This  would  make 
each  individual  muscle  fibre  in  reality  a  separate  muscle. 

Blood  Supply. — A  voluntary  muscle  is  quite  vascular, 
each  fibre  being  invested  with  a  capillary  net-work  almost 


MUSCLES   AND    PHENOMENA    OF   CONTRACTION.         117 

along  its  entire  length.    These  capillaries,  together  with  the 


Fig.  61.— SHOWING  THE  MANNER  IN  WHICH  THE  CAPILLARIKS  ARK  SUPPLIED  TO  THE 

VOLUNTARY   FIBRES.      (E-  A.  S.) 

nerves,   are  carried  by  the  connective  tissue   perimysium , 
which  wraps  more  or  less  completely  each  individual  fibre. 

Nerves. — Each  muscle  fibre  is  connected  with  a  nerve. 
The  nerve  penetrates  the  sarcolemma  and  then  has  its  axis 


Fig.  62.— MUSCLE  FIBRES  FROM  A  LIZARD  TO  SHOW  THE  MANNER  OF  TERMINATION  OF 

THE   MOTOR  NERVE   IN  THE   SO-CALLED   "END   ORGANS."      (After  KuhllC.) 

a,  side  view;  b,  surface  view  of  cud  organ. 


118  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

cylinder  expand  into  a  broad  plate-like  structure  known  as 
the  muscle  plate,  or  the  nerve  plate.  In  this  nerve  plate 
occur  numerous  nuclei.  This  nerve  plate  is  probably  noth- 
ing more  than  the  expansion  of  nervous  protoplasm  by 
which  the  contact  between  nerve  and  muscle  is  made  the 
more  intimate. 

Color. — Ordinarily  voluntary  muscles  appear  red.  Ex- 
ceptions to  this  are,  however,  familiar  to  us  all  in  the  case 
of  the  breast  meat  of  domestic  birds,  which  is  white. 
The  redness  of  ordinary  muscle  is  due  to  its  containing 
traces  of  haemoglobin,  which  it  has  probably  derived  from 
the  continued  coursing  of  the  blood  in  such  large  quantities 
through  its  substance.  Muscles  which  are  not  much  used 
and  which,  therefore,  have  their  blood  supply  much  re- 
duced, are  white.  Thus  in  wild  birds  which  use  their 
wings  in  continued  flight,  the  breast  muscles  also  are  dark. 
Whether  this  haemoglobin  is  contained  in  the  muscle  for  a 
specific  purpose,  or  as  a  mere  accidental  coloring,  caused 
by  the  circulating  blood,  is  not  clear.  Possibly  it  may 
enable  the  muscles  to  store  up  in  themselves  for  ready  use, 
a  small  reserve  supply  of  oxygen. 

Growth  of  Muscle. — The  dimensions  of  a  muscle  just 
given  are  by  no  means  invariable.  In  fact,  the  individual 
muscle  fibres  actually  grow  in  size  for  a  long  time,  being 
many  times  larger  in  an  adult  than  in  a  very  young  child. 
The  growth  of  muscle,  resulting  from  continued  properly  di- 
rected muscular  exercise,  such  for  instance  as  with  the 
blacksmith  in  the  use  of  his  arms,  increases  the  size,  and  so 
of  course,  strength  of  the  individual  muscle  fibres  already 
formed.  Reasoning  in  an  opposite  direction,  the  apparent 
atrophy  of.  an  unused  muscle  may  be  due  to  a  peculiar 
shrinking  of  the  individual  muscle  fibres  rather  than  a 
direct  absorption  of  them.  But  it  seems  probable  that  new 
muscle  fibres  may  also  arise  after  birth.  There  are  found 
scattered  throughout  the  muscular  substance  small  spindle- 
shaped  cells,  designated  as  muscle  cells,  or  more  frequently 


MUSCLES   AND   PHENOMENA    OF   CONTRACTION.         119 

on  account  of  their  shape,  spindle  cells.  These  cells  when 
occasions  seem  to  demand  elongate,  their  nuclei  multiply, 
the  external  layer  develops  the  sarcolemma  and  the  interior 
protoplasm,  at  first  structureless,  receives  gradually  the 
characteristic  cross  markings.  These  cross  marks  seem  to 
appear  first  toward  the  outside,  and  later  on  extend  through 
the  middle.  The  nuclei  at  first  distributed  through  the  pro- 
toplasm take  their  position  under  the  sarcolemma,  and  in 
this  way  a  new  muscle  fibre  has  been  produced.  A  sec- 
ond method  of  muscle  formation  is  claimed,  in  which  the 
new  fibres  arise  by  a  longitudinal  splitting  of  old  ones. 
There  is  no  doubt  but  what  under  the  microscope  such 
splitting  fibres  may  be  occasionally  seen,  but  whether  these 
are  fibres  in  process  of  formation,  or  whether  they  may  not 
be  fibres  that  are  undergoing  degeneration,  is  a  question 
still  unsolved. 

THE  FINER  STRUCTURE  OF  THE  MUSCLE  FIBRE. 

The  histological  points  mentioned  so  far  may  be  made 
out  without  any  question  by  any  good  observer  possessed 
of  a  good  compound  microscope.  But  when  we  have  seen 
the  muscle  composed  of  alternating  light  and  dark  bands, 
it  has  not  yet  been  made  out  to  what  kind  of  a  structure 
this  appearance  is  due.  On  account  of  the  extreme  mi- 
nuteness it  is  difficult  to  establish  the  ultimate  structure  very 
plainly,  so  that  what  is  given  in  explanation  of  its  finer 
anatomy  is  to  a  large  extent  theory. 

A  single  fibre  is  easily  seen  to  consist  of  still  finer  fib- 
rils, as  is  evidenced  by  the  fact  that  the  ends  of  a  fibre  will 
fibrillate  out  into  delicate  fibrils,  much  like  an  ordinary 
twisted  rope  when  its  end  is  unwound.  These  finer  threads 
are  called  fibrils,  and  bundles  of  them  are  believed  to  make 
each  individual  muscle  fibre.  But  when  subjected  to  cer- 
tain chemical  agents  a  muscle  fibre  may  also  be  made  to 
split  horizontally  into  small  disks  somewhat  like  the  stack 
of  coin  referred  to,  might  be  thrown  over  and  fall  into  the 
individual  pieces.  This  would  seem  to  show  that  the  fibrils 


120  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

themselves  are  made  up  of  component  pieces,  in  some  way 
attached  end  to  end  to  make  up  the  entire  length.  These 
component  parts  of  each  fibril  are  called  the  muscular  units 
or  the  sarcomeres.  When  the  muscle  fibres  break  up  into 
these  disks  the  line  of  cleavage  runs  through  the  middle  of 
the  light  band.  With  very  high  powers  there  may  be  dis- 
cerned at  this  point  a  little  darker  line,  which  is  probably  a 
membrane,  and  has  been  called  Krause's  membrane.  In 
the  longitudinal  splitting  of  the  fibre  into  the  fibrillse,  such 
as  a  specimen  of  muscle  hardened  in  alcohol  readily  does, 
the  lines  of  splitting  seem  to  be  in  a  peculiar  inter-columnar 
substance  which  binds  the  individual  fibrils  together. 

From  these  two  manners  of  breaking  up  it  can  easily  be 
seen  that  the  individual  sarcomere  is  that  portion  of  a  fibril 
which  extends  from  the  middle  of  one  light  band,  or  from 
Krause's  membrane,  to  the  middle  of  the  next  white  band. 
It  is,  therefore,  light  at  both  ends  and  contains  its  dark 
band  in  its  middle.  These  sarcomeres,  lying  in  even  rows, 
give  to  the  entire  muscle  fibre  the  banded  appearance.  The 
light  material  next  to  Krause's  membrane  seems  to  be 
a  thin,  active  kind  of  protoplasm  called  hyaloplasm.  The 
dark  band  in  the  middle  really  consists  of  two  dark  bands 
separated  through  the  middle  by  a  light  band  called  the 
band  of  Hensen.  These  dark  bands,  as  may  easily  be  seen 
by  referring  to  the  diagram,  have  little  comb-like  projec- 
tions extending  up  and  down,  which  next  to  the  band  of 
Hensen  are  united  together  on  each  side  to  a  common  base. 
Whether  these  prongs  or  teeth  are  solid,  or  whether  they 
are  hollow  tubes,  cannot  be  determined.  They  probably 
consist  of  a  firmer  kind  of  protoplasm,  and  are  in  each  sar- 
comere called  the  sarcosome.  The  transparent  columnar 
substance,  which  seems  to  cement  the  individual  fibrillae 
together,  is  of  a  similar  kind  of  protoplasm  called  sarco- 
plasm.  Thus  the  individual  sarcomere  would  have  hyalo- 
plasm at  its  ends,  have  the  sarcosome  or  dark  portion  in 
the  center,  and  be  connected  with  neighboring  sarcomeres 
by  the  intermediate  sarcoplasm. 


MUSCLES    AND    PHENOMENA    OF    CONTRACTION.         121 

When  a  muscle  contracts  it  may  be  seen  that  the  white 
band  becomes  narrower,  but  that  the  teeth-like  projections 
of  the  sarcosome  become  pushed  further  apart  and  dis- 


S.E. 


Fig.  63. — DIAGRAM  OF  A  SINGLK  SARCOMERK. 

A,  in  relaxed  condition;  B,  in  contraction;  K,  K,  membrane  of  Krause;  H,  membrane 
of  Hensen ;  S,  E,  the  darker  sarcous  element. 

tended.  The  phenomena  of  contraction  according  to  this 
view  are  therefore  explained  in  this  manner.  When  a  nerv- 
ous impulse  reaches  the  muscle  directing  it  to  contract,  in 
some  way  yet  entirely  unknown,  the  hyaloplasm  by  its 
activity  flows  in  between  the  prongs  of  the  sarcosome  and 
distends  these.  In  this  way  each  sarcomere  is  slightly 
shortened.  The  multiplication  of  this  shortening  through 
all  of  the  sarcomeres  that  make  up  a  muscle  fibre  produces 
a  movement  of  the  entire  muscle.  Whether  this  hyalo- 
plasm forces  itself  in  between  these  prongs,  or  whether  it 
distends  the  sarcosome  by  flowing  into  these  prongs,  which 
in  the  latter  view  would  be  hollow,  is  not  known.  While 
this  serves  in  a  physical  way  to  make  clear  to  us  the  real 
manner  in  which  a  muscle  fibre  shortens,  it  leaves  as  un- 
answered as  before  what  causes  the  hyaloplasm  in  this 
active  way  to  flow  into  the  sarcosome  and  bulge  it  out 
laterally,  thus  shortening  the  long  diameter  of  the  fibre. 

Plain  Muscular  Tissue. 

Plain  muscular  tissue  also  is  composed  of  fibres;  but 
these  fibres  are  very  much  smaller  than  those  of  voluntary 
muscular  tissue,  and  possess  no  cross  markings  whatever. 
They  are  so  much  smaller  than  the  voluntary  that  on  an 
average  the  length  of  an  involuntary  is  less  than  the  width 
of  a  voluntary.  These  plain  muscle  fibres  are  about  one 


122 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


six-hundredth  of  an  inch  in  length  and  very  narrow,  re- 
sembling elongated  spindles.  They  seem  to  show  a  very 
faint  longitudinal  striation,  and  possess  near  their  center  a 
very  evident  nucleus.  It  is  impossible  to  establish  a  cell 
wall,  like  a  sarcolemma,  though  probably  enveloped  with  a 
dark,  denser  layer.  They  are  never  joined  to  tendons,  but 
are  cemented  together  to  form  sheets  of  muscle.  Bach 
muscle  fibre  is  probably  supplied  with  its  own  nerve;  but 
in  this  case  the  nerve  has  no  end  plate,  but  after  encircling 
the  fibre  once  or  twice  ends  abruptly  in  the  nucleus.  They 
are  not  very  vascular,  and  in  cross-sections  of  involuntary 
muscular  tissue,  the  capillaries  of  which  have  been  injected 
so  as  to  make  them  readily  visible,  there  may  be  as  many 
as  twenty-five  or  thirty  rows  of  plain  cells  between  neigh- 
boring capillaries. 


II 


Fig.  64. — INVOLUNTARY  MUSCLE  FIBRE  CELLS,  FROM  A  HUMAN  ARTERY.     (After  Kb'lliker.) 
a,  nucleus;  ft,  a  fibre  treated  with  acetic  acid  to  render  it  more  transparent. 

These  cells  have  the  power  of  shortening  their  long 
axis,  but  do  not  possess  to  any  such  extent  as  the  volun- 
tary muscles  the  ability  to  contract  quickly  or  energetically. 
They  are  peculiarly  well  adapted  to  the  visceral  organs, 
where  it  is  evident  that  the  movement  ought  to  be  very 
slow,  gradual  and  measured.  Examples  of  this  tissue  may 
be  found  in  the  walls  of  the  stomach  and  intestines,  in  the 


MUSCLES    AND    PHENOMENA    OK    CONTRACTION.         123 

walls  of  the  arteries,  around  the  finer  divisions  of  the  bron- 
chial tubes,  and  in  numerous  other  places. 

Cardiac  Muscle. 

The  third  kind  of  muscular  tissue  occurs  only  in  the 
heart.  The  fibres  in  this  case  are  cross-striped,  very  simi- 
lar to  the  voluntary.  They  are  not  quite  as  wide  as  the 
voluntary,  but  are  very  much  shorter,  a  typical  heart  fibre 
being  usually  only  about  twice  as  long  as  it  is  wide.  It 
possesses  near  its  center  an  evident  nucleus,  in  which  no 
doubt,  the  nerve  ends.  There  are  no  tendons,  but  the 
cells  are  cemented  together  in  bands  of  fibres.  Very  fre- 
quently these  cells  are  branched,  a  property  possessed  by 
neither  of  the  other  kinds  of  fibres.  Because  of  this  cross- 
striation  and  its  size  it  is  evident  that  it  is  an  intermediate 


Fig.  65.— Six  CARDIAC  MUSCLE  FIBRES.     (After  Schafer.) 
b,  c,  showing  branching  of  cells. 

kind  of  muscle  possessing  some  of  the  properties  of  both, 
and  therefore  peculiarly  well  adapted  for  use  in  the  heart, 
where  much  greater  energy  of  contraction  is  desired  than 
in  the  ordinary  involuntary  muscles. 

The  Chemistry  of  Muscle. 

The  muscles    possess    about  seventy-five    per    cent,  of 
water,  traces  of  various  mineral  salts,  bits  of  grape  sugar, 


124  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

and  a  peculiar  kind  of  muscle  sugar  called  inosit:  further, 
traces  of  haemoglobin,  whence  their  color,  bits  of  organic 
compounds  such  as  kreatin,  which  will  be  discussed  further 
in  the  chapter  on  excretion,  and  finally  the  important  sub- 
stance, muscle  albumen.  Just  in  what  form  this  muscle 
albumen  is  in  a  living  muscle  it  is  impossible  to  determine, 
for  in  order  to  investigate  the  albumen  it  is,  of  course, 
always  necessary  to  destroy  the  vitality  of  the  muscle.  If, 
however,  perfectly  fresh  muscle  be  taken  and  then  cooled 
almost  to  the  freezing  point,  then  cut  into  small  pieces  and 
the  liquid  pressed  out  through  a  cloth,  there  may  be  filtered 
out  in  this  way  a  slightly  yellowish-colored  fluid  called 
muscle  plasma.  This  muscle  plasma  at  ordinary  tempera- 
tures coagulates  much  like  the  blood,  and  soon  presses  out 
of  itself  a  serum  much  like  a  blood  clot  would,  which  serum 
is  called  muscle  serum.  The  substance,  which  forms  the 
solid  portion  of  the  clot,  is  familiar  to  all  students  of  physi- 
ology under  the  name  of  myosin.  This  myosin  is  insoluble 
in  water,  but  soluble  in  common  salt  solutions,  and  also 
soluble  in  dilute  acids.  When  dissolved  in  dilute  acids  it 
is  changed  into  syntonin,  which  is,  therefore,  in  reality 
merely  an  acid  solution  of  myosin.  The  blood  plasma 
which  has  been  pressed  out  of  the  clot  contains  several 
albumens,  the  principal  one  being  ordinary  serum  albumen. 
The  nutritive  value  of  muscles  is  derived,  to  a  large 
extent,  from  these  albumens.  As  most  of  them  are,  how- 
ever, insoluble  in  water  and  easily  coagulated  by  heat,  but 
little  of  the  albumens  is  removed  by  boiling.  The  mineral 
salts  and  the  flavors  are  of  course  easily  extracted  by  boil- 
ing water,  and  so  may  give  to  the  liquid  quite  a  strong 
taste,  which  may  mislead  the  person  into  the  belief  that  the 
strong  taste  is  an  evidence  of  its  nutritive  value.  It  is  well 
to  bear  this  in  mind,  as  attempts  are  frequently  made  to 
nourish  people  on  variously  prepared  soups  and  broths,  in 
the  belief  that  the  boiling  of  the  meat  has  extracted  from 
it  its  nutritive  ingredients.  A  little  of  the  albumen  may  pos- 
sibly thus  be  extracted,  but  the  nutritive  property  of  it  is 


MUSCLES   AND    PHENOMENA    OF    CONTRACTION.         125 

obtained  only  in  the  digestion  of  the  muscle  substance 
itself.  Special  preparations  of  broth  in  which  the  muscle 
substance  has  been  at  first  digested  artificially,  and  thus 
made  an  ingredient  of  the  broth  have,  of  course,  their  full 
nutritive  value. 

Elasticity. 

The  ordinary  muscles  possess  to  some  extent  an  elas- 
ticity which  enables  them  when  they  are  stretched  by  any 
weight  to  return  to  their  former  position  as  soon  as  the 
stress  is  removed.  Naturally  in  the  body  all  muscles  are 
slightly  stretched,  even  when  entirely  relaxed,  for  a  muscle 
cut  from  one  of  its  connections  at  once  draws  up  and 
becomes  materially  shorter.  This  is  one  of  the  dangers 
accompanying  the  fracture  of  a  bone,  for  as  soon  as  the 
controlling  action  of  the  bone  is  destroyed  the  muscles  pull 
themselves  together,  and  so  the  ends  of  the  bone  may  be 
materially  displaced.  The  advantage  of  having  the  muscles 
on  a  stretch  all  the  time  is,  that  as  soon  as  they  begin  to 
contract  they  begin  to  pull  upon  the  bones  at  once  and  no 
time  or  energy  is  lost  in  first  pulling  up  any  slack  of  the 
muscle  itself. 

Physiology  of  Muscular  Contraction. 

Thus  far  the  muscle  has  been  considered  as  an  inert 
structure,  and  all  that  has  been  said  would  apply  to  a  dead 
muscle  as  well  as  one  still  living.  But  living  muscles 
possess  the  property  to  contract  when  they  are  properly 
stimulated. 

MUSCLE   STIMULI. 

The  usual  stimulus  to  usher  in  a  muscular  contraction 
is  a  nerve  stimulus,  but  it  may  be  stimulated  in  other  ways. 
First,  by  mechanical  stimuli:  Sudden  pressure,  tearing, 
pricking,  etc.,  produce  each  time  a  contraction  of  the 
affected  muscle.  Second,  thermal  stimuli:  A  sudden  change 
of  temperature  causes  the  muscles  to  contract.  The  limits 
of  such  changes  are  from  almost  freezing  up  to  about  one 
hundred  and  ten  degrees.  Above  and  below  these  tern- 


126  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

peratures  the  muscles  cease  to  react.  Third,  chemical 
stimuli:  A  number  of  chemical  agents  will  stimulate  the 
muscles.  Such  agents  are  fumes  of  nitric  oxide,  sulphur 
dioxide,  hydrochloric  acid,  but  especially  ammonia  gas. 
Fourth,  electrical  stimuli:  A  current  of  electricity  may 
in  different  forms  induce  the  muscles  to  very  vigorous 
activity,  and  one  of  the  best  worked-out  chapters  on  muscle 
physiology  is  its  reaction  to  electrical  stimuli. 

The  question  whether  these  stimuli  affect  the  muscles 
themselves,  and  not  the  nerves  in  the  muscles,  can  be  defi- 
nitely answered  by  saying  that  the  stimuli  affect  the  muscles 
themselves  directly.  For  instance,  ammonia  stimulates  the 
muscles,  but  does  not  affect  the  nerve.  Still  again  some 
muscles,  for  instance  the  sartorius  of  the  thigh,  have  no 
nerves  in  their  ends,  yet  the  muscle  there  may  be  stimu- 
lated to  contraction.  The  best  proof  is,  however,  that 
furnished  by  the  South  American  poison  called  curare. 
This  curare  lames  the  motor  nerves,  but  a  muscle  with  such 
a  lamed  nerve  will  still  react  to  all  of  the  preceding  stimuli. 
This  curare  is  used  by  many  of  the  South  American  Indians 
in  their  chase  and  warfare.  The  end  of  the  arrow  is  im- 
pregnated with  the  curare,  and  when  the  arrow  is  intro- 
duced into  the  flesh  of  an  animal  it  drops  down  motionless 
to  the  ground.  Its  circulation  and  all  of  its  sensory  nerves 
are  left  intact,  but  there  is  a  complete  paralysis  of  all  vol- 
untary action.  The  animal  of  course  dies  by  suffocation, 
being  unable  to  move  the  muscles  of  respiration. 

A    SINGLE    CONTRACTION. 

Having  now  called  attention  to  the  stimuli  which  produce 
muscular  contraction,  a  closer  study  of  such  a  contraction 
itself  naturally  follows.  If  in  order  to  study  it  more  advan- 
tageously, a  frog's  muscle  be  entirely  cut  out  from  the  body 
and  then  suspended  from  a  hook,  it  may  still  be  made  to 
contract,  and  on  account  of  its  isolation,  the  phenomena  of 
such  a  contraction  much  better  studied.  Usually  a  piece  of 
nerve  running  to  the  muscle  is  left  connected  with  it  and 


MUSCLES    AND    PHENOMENA   OF    CONTRACTION.         127 

the  stimuli  are  applied  to  the  nerve,  and  through  this  the 
muscle  induced  to  contract.  If  now  such  a  muscle  makes  a 
contraction,  the  same  occurs  with  such  rapidity  that  to  the 
unaided  eye  it  seems  but  a  rapid  shrinking  and  a  return  to 
its  former  position.  If,  however,  the  lower  end  of  the 
muscle  be  fastened  to  a  lever,  and  this  lever  be  made  to 
write  on  a  drum  revolving  at  a  known  speed,  the  contrac- 
tion will  pull  the  muscle  and  consequently  the  lever  up,  and 
a  curve  will  be  described  on  the  revolving  surface.  On  this 
curve  the  various  phenomena  are  then  at  leisure  determin- 
able.  The  arrangement  for  such  a  demonstration  may  be 
seen  in  the  accompanying  diagram. 


Fig.  66.— ARRANGEMENT  FOR  SECURING  MYOGRAMS. 

P,  the  moving  recording  surface,  which  by  the  projection  at  d  opens  the  circuit  in  K 
at  c,  and  so  induces  a  break  current  iap  which  passing  through  the  muscle  stimulates  it. 
In  this  way  the  moment  of  stimulation  is  determined  exactly,  it  being  the  moment  of 
contact  of  d  with  c.  The  curve  is  then  recorded  as  in  figure. 

If  now  the  exact  moment  be  noted  at  which  the  impulse 
reaches  the  muscle  it  is  found  that  the  muscle  does  not  con- 
tract at  once,  but  that  there  is  a  short  period  after  the  im- 
pulse reaches  the  muscle  before  it  begins  to  shorten.  This 
period  is  about  one-hundredth  of  a  second,  and  is  called  the 
latent  period.  During  this  period  the  nervous  impulse  has 
probably  originated  molecular  changes  in  the  muscle  pre- 
paratory to  the  contraction.  The  latent  period  is  succeeded 
by  a  steady  contraction  of  the  muscle  to  a  maximum,  fol- 
lowed by  the  relaxation  of  the  muscle  to  its  original  position. 


128  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

This  movement  up  and  down  occupies  about  nine-hun- 
dredths  of  a  second,  making  the  entire  time  about  one-tenth 
of  a  second.  Just  what  these  molecular  changes  in  the 


Fig.  67. — CURVE  OF  A  SINGLE  CONTRACTION. 

R,  a,  the  latent  period;  a,  6,  the  gradual  contraction  to  a  maximum;  b,  c,  the  some- 
what more  sudden  relaxation ;  c,  d,  a  slight  rise  owing  to  the  inertia  of  the  recording 
lever,  and  having  nothing  to  do  with  the  muscle  contraction  itself. 

muscle  are,  which  occur  during  the  latent  period,  it  is  im- 
possible to  tell,  but  it  is  interesting  to  note  that  by  means 
of  a  galvanometer  (an  instrument  for  detecting  currents  of 
electricity)  electrical  currents  are  indicated  in  the  muscle 
running  from  the  parts  furthest  removed  from  the  nerve  to 
the  part  directly  stimulated  by  the  nerve.  These  currents 
are  called  the  currents  or  waves  of  negative  variation.  What 
meaning  these  currents  have  which  flow  in  a  muscle  during 
the  latent  period  is  not  known,  but  they  are  external  evi- 
dences of  complicated  molecular  changes  in  the  muscle  sub- 
stances itself,  which  make  possible  the  succeeding  contrac- 
tion. Such  a  contraction  which  follows  a  single  stimulus 
is  called  a  simple  contraction.  Such  a  simple  contraction 
occurs,  as  long  as  the  vitality  of  the  muscle  is  left  intact, 
as  often  as  a  stimulus  is  applied.  If,  however,  the  stimuli 
are  applied  so  rapidly  that  the  second  stimulus  enters  the 
muscle,  before  the  relaxation  from  the  first  stimulus  has 
occurred,  the  muscle  contracts  still  more.  It  is,  so  to  speak, 
a  superposition  of  the  second  contraction  upon  the  first. 
Such  a  superposition  does  not,  however,  go  on  indefinitely; 
that  is,  there  cannot  be  super-imposed  a  third  onto  a  second, 
or  a  fourth  onto  a  third  indefinitely,  for  soon  a  maximum  is 
reached  beyond  which,  no  matter  how  many  stimuli  are  sent 
in,  the  muscle  will  not  contract. 


MUSCLES    AND    PHENOMENA    OF    CONTRACTION.         129 
TETANIC   CONTRACTIONS. 

But  with  very  rapidly  entering  stimuli  the  muscle  re- 
mains in  one  spasmodic  contraction.  Such  a  continued  and 
uninterrupted  contraction  is  spoken  of  as  a  tetanus.  All 
the  contractions  of  muscles  caused  by  the  will  are  such 
tetanic  contractions,  for  the  impulses  sent  along  voluntary 
paths  to  our  muscles  are  sent  at  the  rate  of  about  ten  per 
second.  The  fact  that  a  voluntary  muscle  receiving  im- 
pulses at  such  a  constant  rate  does  not  remain  in  one  con- 
tinuous and  constant  contraction,  is  due  to  the  fact  that 
although  the  rate  of  the  stimuli  remains  the  same,  the  force 
of  these  stimuli  may  vary,  and  so  the  force  of  the  con- 
traction varies  accordingly. 

THE    WAVE   OF  CONTRACTION. 

When  a  stimulus  reaches  a  muscle  the  entire  muscle 
does  not  begin  to  contract  at  once,  but  the  contraction  pro- 
ceeds in  the  form  of  a  wave,  beginning  at  the  point  where 
the  impulse  enters  and  extending  to  the  opposite  ends. 
Somewhat  like  a  wave  in  a  trough  of  water  caused  by  the 
introduction  of  a  pebble,  starts  at  the  point  where  the  peb- 
ble strikes  it  and  proceeds  from  this  point  in  opposite  direc- 
tion to  the  ends  of  the  trough.  That  is  to  say,  the  part  of 
the  muscle  next  to  the  nerve  begins  to  shorten,  and  then  in 
consecutive  order  portions  further  away  from  it  follow.  This 
wave  of  contraction  can  be  easily  noticed  on  a  muscle  as  a 
little  swelling  which  runs  from  the  insertion  of  the  nerve  to 
the  opposite  ends.  This  rate  has  been  measured,  and  is 
in  the  living  muscle  (not  cut  out  of  the  body)  about  thirty 
or  forty  feet  per  second,  while  in  muscles  which  have  been 
cut  out  of  the  body,  on  account  of  their  reduced  vitality,  it 
is  only  about  fifteen  feet  per  second.  In  plain  muscle  tissue 
the  rate  of  such  a  wave  reaches  the  low  minimum  of  three 
to  four  inches  per  second.  Such  a  wave  of  contraction  in 
plain  muscular  tissue  may  be  easily  seen  in  the  creeping 
peristaltic  motion  of  the  intestine.  The  phenomena  here 

described  and  the  times  in  which  they  occur  apply  only  to 
9 


130  STUDIES    IN   ADVANCED   PHYSIOLOGY. 

living  muscles.  Muscles  which  have  begun  to  die,  or  have 
been  fatigued  by  excessive  work,  or  have  been  cooled  too 
much,  or  have  been  heated  to  above  one  hundred  and  ten 
degrees,  react  much  more  slowly,  and  finally  refuse  to  act 
at  all. 

The  Actual  Lifting  Power  of  Muscles. 

It  is  the  function  of  muscles  to  pull  and  lift,  and  their 
maximum  capacity  to  lift  is  of  course  a  matter  of  general  in- 
terest. The  amount  which  a  muscle  can  lift  varies  with  its 
cross-section  in  the  same  way  that  the  capacity  of  a  rope  to 
sustain  a  weight  depends  upon  the  thickness  of  the  rope. 
With  frog's  muscle,  experiments  indicate  that  a  muscle  a 
square  centimeter  in  cross-section  can  lift  about  six  and  one- 
half  pounds.  A  square  centimeter  of  muscle  in  man  may 
lift  as  much  as  twenty-five  pounds  under  the  stimulus  of  the 
will.  When  we  remember  that  some  muscles  are  many 
square  centimeters  in  cross-section  the  force  with  which  they 
may  be  made  to  lift  and  pull  is  easily  explained. 

Amount  of  Shortening  of  Muscles. 

Another  question  of  interest  is  the  proportionate  length 
to  which  a  muscle  may  contract  itself.  This,  of  course, 
varies  somewhat  with  different  muscles.  A  short,  thick 
muscle  would  not  shorten  itself  as  much  as  a  longer  slender 
muscle.  Varied  experiments  indicate  that  the  actual  reduc- 
tion in  length  may  be  from  sixty-five  to  eighty-five  per  cent, 
of  the  entire  muscle. 

Changes  in  Volume. 

A  muscle  when  it  contracts  occupies  a  little  less  volume 
than  it  did  in  an  expanded  state.  This  is  no  doubt  due  to 
the  fact  that  in  the  contraction,  some  of  the  muscle  sub- 
stance is  more  compressed.  This  may  be  easily  demon- 
strated by  hanging  a  muscle  in  a  vessel  of  water  and  then 
making  it  contract.  On  the  contraction,  the  height  of  the 
water  in  the  vessel  sinks  a  trifle. 


MUSCLES   AND    PHENOMENA   OF   CONTRACTION.         131 

Muscle  Fatigue. 

One  of  the  most  familiar  phenomena  of  our  muscles  is 
their  fatigue  resulting  from  hard  work.  This  fatigue  is 
caused  by  an  accumulation  of  waste  matter  in  the  muscle 
substance,  owing  to  its  active  work.  This  may  be  easily 
demonstrated  by  taking  a  frog's  muscle,  and  causing  it  to 
contract  until  it  is  thoroughly  fatigued  and  refuses  to  react 
to  further  stimuli.  If  now  such  a  muscle  be  washed  with 
water  which  contains  a  little  salt,  so  as  to  make  the  water 
as  nearly  like  blood  serum  as  possible  in  that  respect,  it 
begins  to  contract  again  with  apparently  renewed  energy. 
The  only  explanation  available  is  that  the  salt  water  in 
question  washed  out  some  of  the  waste  products.  Of  course 
this  could  not  be  continued  indefinitely,  for  soon  the  muscle 
fibre  not  being  nourished  would  be  robbed  of  all  its  mate- 
rial, and  so  a  final  exhaustion  ensue.  This  explains  why  a 
muscle  fatigued  revives  so  quickly  when  it  is  moved  about 
freely,  and  for  a  few  minutes  the  blood  is  allowed  to  stream 
into  it  uninterruptedly.  This  feeling  of  fatigue,  however, 
does  not  come  directly  from  the  muscles.  The  muscle  fibres 
are  supplied  with  motor  nerves  only,  and  it  is  probably  im- 
possible to  receive  a  sensory  impression  from  them.  There 
are,  however,  distributed  between  the  muscle  fibres  sensory 
nerves,  and  from  these  we  derive  our  muscular  sensations. 
Some  of  these  nerve  fibres  seem  to  end  in  little  special  end 
organs  which  suggest  the  Pacinian  bodies  of  the  mesentery. 
In  fact,  some  histologists  believe  that  the  spindle  cells  men- 
tioned on  a  preceding  page*  as  cells  which  develop  later  in- 
to new  muscle  fibres,  are  not  muscle  cells  at  all,  but  are 
sensory  cells  connected  with  nerves,  and  that  from  these 
to  a  large  extent  we  get  our  muscular  sensations. 

The  Blood  Supply. 

The  vitality  of  a  muscle  is  very  dependent  upon  its  blood 
supply.  If  the  artery  going  to  a  muscle  be  cut,  or  if  only 
venous  blood  be  able  to  reach  it,  the  muscle  at  once  begins 

*See  page  119, 


132 


STUDIES   IN   ADVANCED    PHYSIOLOGY. 


to  atrophy.  There  is  in  the  body  a  nervous  arrangement 
by  which  the  blood-vessels  leading  to  the  muscle  are  at 
once  enlarged  as  soon  as  that  muscle  is  called  into  action. 
These  are  the  dilator  nerves,  which  will  be  treated  in  detail 
in  the  chapter  on  circulation.  By  this  arrangement  a  work- 
ing muscle  receives  an  extra  amount  of  nourishment,  and 
of  oxygen,  to  carry  on  its  added  work.  The  vitality  of  a 
muscle  seems  also  to  be  dependent  upon  its  connection  with 
the  nervous  system.  A  muscle  with  its  nerve  cut  begins  to 
atrophy  at  once.  The  fibres  become  shrunken  and  turbid, 
and  soon  lose  their  power  of  contractility.  This  explains 
why  in  persons  suffering  with  paralysis  the  muscles  begin 
so  rapidly  to  shrink  and  weaken. 

Electrical  Phenomena  in  Muscles. 

When  a  muscle  is  cut  out  of  the  body  and  tested  with  a 
galvanometer  there  may  be  demonstrated  running  through 
its  substance  small  currents  of  electricity.  The  central  or 
uncut  portion  of  the  muscle  seems  to  be  positive  with  refer- 
ence to  the  cut  ends.  Thus,  if  the  wires  be  placed  one  on 
the  center  of  the  muscle  and  the  other  at  the  end,  a  current 
runs  through  the  wires  from  the  central  portion  toward  the 
ends,  and  of  course  in  the  muscle,  to  complete  the  circuit, 
from  the  ends  toward  the  center.  These  currents  have  been 


Fig.  68.— DIAGRAM  TO  SHOW  THE  DIRECTION  OF  THE  MUSCLE  CURRENTS  IN  AN-  EXCISED 

MUSCLE. 

e,f,  central  positive  portion;  o,  c,  b,  d,  cut  negative  ends.  The  lines  with  arrows  in- 
dicate the  direction  a  current  would  take  between  the  points  touched.  In  lines  6,  7,  8,  no 
current  appears  for  obvious  reasons. 


MUSCLES    AND    PHENOMENA    OF   CONTRACTION.         133 

called  the  muscle  currents.  They  have,  however,  probably 
no  real  physiological  significance,  because  it  has  been  found 
in  many  different  fields  that  a  tissue  which  is  injured  and 
dying  becomes  electrically  negative  to  tissues  left  unhurt. 
As  the  muscle  where  it  was  cut  at  the  ends  has  begun  to 
die,  these  ends  have  become  negative  with  reference  to  the 
central  unhurt  portion.  For  this  reason  when  connections 
are  made  currents  circulate.  These  currents  are,  conse- 
quently, not  found  in  living  muscle,  because  in  this  latter 
case  there  are  no  dying  portions  to  be  negative. 

WAVE  OF  NEGATIVE  VARIATION. 

If  now,  such  a  cut-out  muscle  be  connected  with  the 
galvanometer,  and  the  presence  of  the  current  circulating 
through  it  indicated  by  the  rotation  of  the  magnetic  needle, 
and  if  while  this  is  going  on,  the  muscle  be  stimulated  to 
contraction,  it  is  found  that  during  the  latent  period  the 
needle  tends  to  swing  back  to  its  original  position.  This 
indicates  that  during  this  latent  period  there  must  have 
been  set  up  in  the  muscle  substance  currents  of  electricity 
which  run  counter  to  the  first  currents,  and  so  neutralize 
them  to  some  extent,  causing  the  needle  to  swing  back 
toward  its  resting  point.  This  current  is  called  the  wave  of 
negative  variation.  This  wave  is  explained  on  grounds  sim- 
ilar to  that  of  the  ordinary  muscle  currents.  The  muscle 
substance  not  only  when  dying,  but  also  when  stimulated, 
becomes  negative  at  such  points.  As  the  nerve  enters  the 
muscle  near  the  middle,  and  as,  therefore,  the  point  of 
stimulation  arises  here,  this  becomes  negative  toward  the 
ends  of  the  fibres  which  the  stimulus  has  not  yet  reached. 
Thus  there  will  be  set  up  counter  currents  tending  to  run 
from  the  more  positive  ends  to  the  negative  middle.  But 
as  these  run  in  exactly  the  opposite  direction  to  the  cur- 
rents caused  by  the  dying  negative  ends,  they  tend  to  neu- 
tralize each  other  more  or  less,  and  so  the  needle  swings 
back  toward  the  resting  point. 


134  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

This  wave  of  negative  variation  referred  to  occurs  in  liv- 
ing muscle,  and  its  presence  there  may  be  indicated  by  a 
sensitive  galvanometer.  The  rate  of  this  wave  has  been 
measured,  and  is  in  the  muscles  of  mammals  about  three 
meters  per  second.  The  time  required  for  this  wave  to 
traverse  the  entire  muscle  is  only  about  one  three-hun- 
dredths  of  a  second.  As  the  latent  period  is  about  one  one- 
hundredth  of  a  second,  this  wave  of  negative  variation  is 
entirely  over  before  the  wave  of  contraction  follows. 

This  wave  then  has  physiological  meaning.  The  deflec- 
tion of  the  magnetic  needle  connected  with  the  muscle  in- 
dicates that  there  are  going  on  in  this  latent  period  peculiar 
molecular  changes,  the  nature  of  which  we  do  not  yet  at  all 
understand,  but  which  get  the  muscle  ready  for  the  con- 
traction which  follows  just  an  instant  later.  This  wave  run- 
ning along  a  muscle  may  be  actually  used  to  stimulate  the 
nerve  of  another  muscle.  If,  for  instance,  two  muscles 
with  their  nerves  intact  be  removed  from  a  frog,  which 
muscles  we  will  call  here  A  and  B,  and  the  nerve  of  A  be 
laid  on  the  muscle  of  B,  and  then  the  nerve  of  B  stimulated 
so  that  B  will  contract,  it  is  found  that  not  only  does  B  con- 
tract, but  A  contracts  also.  This  is  explained  in  this  way: 
"Every  time  B  is  stimulated  by  its  nerve  a  wave  of  negative 
variation  runs  along  it,  which  wave  acts  as  an  electrical 
stimulus  to  the  nerve  of  A  which  rests  on  it,  and  so  the 
nerve  of  A,  being  stimulated,  produces  a  contraction  of  the 
muscle  of  A.  If,  then,  B  is  tetanized,  a  corresponding  te- 
tanus is  produced  in  A,  showing  that  each  single  impulse 
has  its  own  wave  of  negative  variation  preceding  it. 

Rigor  Mortis,  or  Death-Stiffening. 

Soon  after  death,  varying  from  a  few  minutes  to  not 
more  than  several  hours,  the  muscles  of  the  body  become 
intensely  rigid,  preventing  the  bending  at  the  joints,  a  con- 
dition familiar  as  ' '  death-stiffening, ' '  or  rigor  mortis.  This 
rigor  begins  as  a  rule  in  the  muscles  of  the  lower  jaw  and 
neck,  then  seizes  the  upper  extremities  and  gradually  ex- 


MUSCLES   AND    PHENOMENA   OF   CONTRACTION.         135 

tends  to  the  lower  extremities.  After  some  time  this  rigor 
begins  to  disappear  and  the  dead  body  again  becomes  mov- 
able at  its  joints.  This  loosening  is  usually  attributed  to 
the  beginning  stage  of  decomposition,  but  this  is  probably 
not  right.  According  to  the  more  general  explanation  rigor 
mortis  is  due  to  the  clotting  of  the  muscle  plasma.  Such  a 
formation  of  a  solid  muscle  clot  would  of  course  at  once  ex- 
plain the  immobility  of  the  body.  A  more  recent  view, 
however,  and  one  which  seems  to  have  most  in  its  favor, 
explains  rigor  mortis  as  a  final  severe  contraction  of  the 
muscles  brought  about  by  the  chemical  changes  which  in- 
duce death.  It  would  be,  in  other  words,  a  severe  tetanus 
produced  by  a  series  of  disintegrating  chemical  changes 
which  accompany  the  dissolution  of  life.  According  to 
this  view  the  relaxation  which  follows  after  the  rigor  would 
be  merely  a  return  of  these  muscles  to  their  relaxed  condi- 
tion. That  this  rigor  is  probably  a  contraction  and  not  a  mere 
coagulation  of  internal  albumens  is  further  supported  by  the 
fact  that  a  good  deal  of  heat  is  liberated,  and  that  the 
muscles  show  all  those  phenomena  which  accompany  ordi- 
nary severe  contraction. 

The  Source  of  Muscular  Energy. 

The  view  that  muscles  possessed  a  kind  of  vital  energy, 
which  of  course  Could  not  therefore  be  measured  like  or- 
dinary physical  energies,  has  long  been  abandoned,  and  we 
know  now  that  muscles  must  derive  their  energy  to  contract 
in  accordance  with  the  same  laws  that  determine  what  the 
energy  -  yielding  power  of  an  ordinary  steam  engine  or 
dynamo  shall  be.  Muscle  energy  is  identical  per  se  with 
physical  and  chemical  energies.  The  question  now  arises, 
in  what  manner,  from  the  material  that  is  carried  to  it  by  the 
blood,  does  it  get  its  energy  to  produce  heat  and  motion? 
Without  going  into  a  discussion  of  older  views,  the  follow- 
ing seems  the  explanation  most  in  accord  with  all  the  ob- 
served facts. 


136  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

When  a  muscle  contracts  some  of  its  living  muscle  sub- 
stance disintegrates  into  simpler  compounds,  and  by  this 
disintegration  energy  is  set  free  which  the  muscle  utilizes, 
much  as  in  the  case  of  a  bit  of  nitroglycerine.  The  nitro- 
glycerine disintegrates  into  simpler  chemical  compounds, 
and  by  the  disintegration  a  large  amount  of  energy  is  liber- 
ated to  lift  the  rock,  remove  the  stump,  or  what  not.  A 
muscle  contraction  is,  therefore,  in  reality  a  muscular  sub- 
stance explosion  differing  from  the  nitroglycerine  analogy, 
in  the  fact  that  there  are  but  particles,  here  and  there, 
throughout  its  substance  which  disintegrate,  and  not  the 
entire  muscle  itself.  The  old  view  that  a  muscle  contracts 
because  at  the  time  of  its  contraction  something  is  oxidized 
is  not  correct.  This  may  be  proved  by  removing  from  a 
muscle  all  traces  of  oxygen  and  then  stimulating  it.  It 
will  contract  as  usual.  Muscles  must,  however,  have 
nourishment  and  air  carried  to  them  to  be  built  up,  to  have 
these  wastes  repaired,  but  not  to  produce  the  direct  con- 
traction. As  for  the  same  reason  there  would  have  to  be 
carried  to  the  nitroglycerine  factory  all  the  ingredients  to 
make  nitroglycerine  without  any  intention  whatever  of 
having  the  explosion  occur  by  doing  so. 

Now,  muscle  substance  is  mainly  albuminous.  The 
question  at  once  arises  whether  any  foods  other  than  albu- 
mens may  serve  to  nourish  the  muscles.'  That  other  foods 
may  figure  so  is  argued  by  the  fact  that  most  of  our  muscu- 
lar domestic  animals  are  herbivorous;  that  is,  their  food 
consists  largely  of  other  than  albuminous  material.  There 
seems,  therefore,  a  difficulty  at  first  in  explaining  how 
foods  not  albumens,  that  is,  containing  no  nitrogen,  can  be 
built  into  living  muscle  substance  which  is  albuminous,  that 
is,  which  does  contain  nitrogen.  This  apparent  difficulty 
is  removed,  however,  at  once,  by  observing  that  a  working 
muscle  seems  to  retain  all  the  nitrogenous  products  which 
have  resulted  in  the  muscle  disintegration.  Or,  to  be  more 
explicit  and  to  the  point,  the  living  muscle  albumen  disin- 
tegrates into  products  which  contain  the  nitrogen  and  into 


MUSCLES    AND    PHENOMENA    OF    CONTRACTION.         137 

other  products  free  from  the  nitrogen.  The  main  nitrogen- 
free  product  resulting  from  this  muscular  explosion  is  car- 
bon dioxide  (CO2) ,  which  is  then  eliminated  through  the 
lungs.  The  nitrogenous  products  are,  however,  retained  by 
the  muscle  and  with  nitrogen-free  foods,  such  as  fats  and 
sugars,  may  be  re-combined  to  form  new  living  albumen. 
This  albumen  may  then  disintegrate  a  second  time,  the 
nitrogen-free  products  such  as  carbon  dioxide  may  be  sent 
out,  while  the  nitrogenous  products  are  again  retained,  again 
to  be  united  with  fats  and  sugars  and  built  into  new  muscle 
substance. 

Observations  made  on  working  muscles  are  in  marked 
harmony  with  this  view.  Thus,  every  one  knows  that  the 
harder  one  works  the  more  carbon  dioxide  does  one  breathe 
out  of  the  lungs ;  but  very  careful  experiments  have  shown 
that  the  amount  of  nitrogen  eliminated  through  the  kidneys 
does  not  all  vary  with  the  work  done,  a  man  working  hard 
not  eliminating  any  more  nitrogen  than  one  idle.  If,  of 
course,  all  these  nitrogenous  products  formed  in  the  disin- 
tegration of  muscle  could  be  retained  and  thus  used  over 
and  over  again,  somewhat  like  a  brass  shell  might  be  re- 
loaded and  so  used  over  and  over  again  in  firing,  if  nothing 
were  lost,  there  would  be  no  necessity  in  a  full  grown  man 
of  introducing  new  albumens  into  his  system.  But  in  these 
repeated  disintegrations,  although  most  of  the  nitrogenous 
products  are  saved  and  used  over  and  over  again,  a  little 
incidental  loss,  a  kind  of  wear  and  tear  incident  to  all 
changes  results,  and  it  is  this  little  bit  which  is  then  sent 
to  the  kidneys  finally  be  to  eliminated.  To  replace  this 
wear  and  tear  it  is  absolutely  necessary  to  put  into  the  blood 
new  nitrogen-containing  foods  such  as  albumens.  This  ex- 
plains in  an  unusually  clear  way  how  such  substances  as 
fats,  sugars,  and  the  starches  may  be  gradually  utilized  in 
building  up  muscle  substance.  It  explains  further,  the  im- 
possibility of  doing  without  albumens,  that  is,  nitrogenous 
foods,  altogether.  It  explains  why  the  carbon  dioxide  is  in 
a  general  way  doubled  in  amount  when  the  work  is  doubled. 


138  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

It  explains,  finally,  why  the  working  body  will  eliminate 
practically  no  more  nitrogen  from  the  kidneys  than  an  idle 
one.  Much  in  the  same  way  as  a  machine  standing  still 
may  have  as  much  rust  and  wear  and  tear  in  its  machinery 
as  an  engine  in  proper  use. 

The  reason  at  last  why  in  a  working  muscle  the  arteries 
are  thrown  open  and  the  arterial  blood  carrying  the  oxygen 
and  the  nutritive  substance  of  the  plasma  streams  pell 
mell  through  the  muscle  is,  therefore,  not  to  have  it  con- 
tract the  more,  but  to  give  it  the  opportunity  of  repair- 
ing its  substance  as  rapidly  as  it  is  being  disintegrated. 
The  blood  stream  would  be  like  the  soldier  carrying  the 
ammunition  to  the  gunners,  in  order  that  they  might  make 
good  with  new  powder  the  losses  resulting  in  their  rapid 
firing. 

The  Mechanics  of  the  Muscles. 

THREE  CLASSES  OF  LEVERS. 

With  the  exception  of  a  few  muscles  which  surround 
cavities,  like  the  muscle  around  the  mouth,  all  voluntary 
muscles  are  inserted  into  bones,  and  produce  with  these 
various  kinds  of  levers  used  in  supporting  or  moving  the 
frame.  In  every  lever  there  are  three  points :  the  point  about 
which  the  lever  turns,  called  the  "  fulcrum,"  the  point  at 
which  the  weight  is  placed,  and  the  point  at  which  the 
power  is  applied.  According  to  the  way  in  which  these 
three  points  are  grouped,  levers  are  divided  into  those  of 
the  first  class,  the  second  class,  and  the  third  class.  In  a 
lever  of  the  first  class  the  fulcrum  lies  between  the  "power" 
and  the  "weight."  A  familiar  illustration  of  such  a  lever 
is  found  in  the  ordinary  weighing  balance,  which  is  a  beam 
suspended  in  the  middle  from  a  fixed  point,  the  fulcrum, 
while  the  ' '  weight ' '  and  the  ' '  power  ' '  are  applied  at  the 
opposite  ends.  Numerous  other  illustrations  might  be  ad- 
duced. The  further  illustration  of  the  teetering-board  will 
suffice.  There  are  few  levers  of  this  kind  in  the  body. 
The  nodding  of  the  head  is  one.  In  this  instance  the  ful- 
crum is  at  the  point  where  the  occipital  bone  rests  on  the 


MUSCLES    AND    PHENOMENA    OF   CONTRACTION.         139 

atlas,  the  power  is  applied  where  the  muscles  of  the  neck 
are  inserted  into  the  skull,  while  the  final  weight  of  the 
head  might  represent  the  "weight."  A  second  illustra- 
tion of  this  lever  is  found  in  the  act  of  bowing.  In  this 
case  the  fulcrum  is  at  the  hip  joint,  the  "power  "  is  applied 
where  the  muscles  of  the  hip  are  inserted  to  pull  the  body 
backwards,  while  the  forward  weight  of  the  body  represents 
the  "weight."  In  such  a  lever  little  is  gained  except  a 
change  of  direction;  a  power  pulling  down  may,  with  such 
a  lever,  pull  a  weight  up. 

In  a  lever  of  the  second  class  the  ' '  weight ' '  is  between 
the  fulcrum  and  the  u  power."  The  ordinary  wheelbarrow 
is  a  lever  of  this  class,  having  its  fulcrum  at  the  forward 
wheel,  the  "  weight "  in  the  bed,  and  the  "  power  "  applied 
where  the  hands  grasp  the  handles.  A  crowbar  in  prying 
upwards,  as  in  rolling  a  barrel,  is  a  further  illustration. 
There  are  not  very  many  levers  of  this  order  in  the  body. 
The  best  illustration  of  this  lever  is  found  in  the  ankle. 
When  the  body  is  lifted  the  toes  become  the  fulcrum,  the 
weight  of  the  body  rests  on  the  astragalus,  while  the 
4 '  power ' '  is  applied  at  the  end  of  the  heel  where  the  ten- 
don Achilles  of  the  calf  of  the  leg  is  applied.  It  is  evident 
that  by  means  of  such  a  lever  a  greater  weight  may  be  lifted 
than  the  power  could  lift  directly,  for  the  experience  of 
everyone  will  convince  him  that  by  means  of  a  wheel- 
barrow a  man  may  lift  a  greater  load  than  he  could  by 
directly  hoisting  it  with  his  arms. 

A  lever  of  the  third  class  has  the  ' '  power  ' '  between  the 
fulcrum  and  the  weight.  Most  of  the  levers  of  the  body  are 
of  this  kind.  The  flexing  of  the  forearm  at  the  elbow  is  an 
illustration  of  this  class.  Here  the  fulcrum  is  at  the  elbow, 
the  weight  is  in  the  hand  where  the  object  to  be  lifted  is 
held,  and  the  power  where  the  tendon  of  the  biceps  muscle 
is  imbedded  in  the  radius.  It  is  evident  that  in  such  a 
muscle  much  power  is  lost,  for  the  muscle,  in  order  to  raise 
a  certain  weight  at  the  end  of  the  radius,  would  have  to 
pull  much  more  than  that  weight  by  pulling  on  the  radius 


140  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

near  the  elbow.  Just  as  it  is  more  difficult  to  lift  a  heavy 
weight  on  the  end  of  a  long  fork  than  it  would  be  to  pick  it 
up  directly.  But  while  such  power  is  lost,  rapidity  of  mo- 
tion is  gained,  but  a  slight  contraction  of  the  biceps  muscle 
causing  the  hand  to  move  through  quite  a  distance.  Such 
arrangements  in  our  bodies  indicate  that  the  levers  were 
intended  rather  for  dexterity  and  rapidity  of  motion  than 
for  the  ability  to  lift  mere  weights.  However,  in  the  case 
of  the  ankle,  at  which  point  we  have  to  lift  at  each  step 
the  weight  of  the  entire  body,  a  lever  of  the  second  class  is 
put,  an  arrangement  by  which  a  person  is  never  obliged  to 
pull  as  much  on  his  muscles  as  the  weight  of  his  body 
actually  is. 

THE  MATHEMATICS  OF  LEVEES. 

In  every  lever,  no  matter  whether  of  the  first,  second  or 
third  class,  the  distance  from  the  power  to  the  fulcrum  is 
called  the  "power-arm"  (pa) ,  while  the  distance  from  the 
"weight"  to  the  fulcrum  is  called  the  "weight-arm"  (wa) . 
In  all  three  classes  of  levers  the  following  simple  arithmeti- 
cal proportion  holds  true:  That  the  P:  W:  \wa:pa.  Hence, 
if  three  of  these  factors  are  given,  by  the  simplest  mathemat- 
ical process  the  fourth  may  be  determined.  To  illustrate  in  a 
specific  case :  If  we  assume  in  the  case  of  the  foot  the  dis- 
tance from  the  toes  to  the  astragalus  to  be  seven  inches, 
and  the  distance  from  this  point  in  the  astragalus  to  the 
point  where  the  tendon  is  attached  to  the  heel  bone  two 
inches,  we  have  the  power-arm  of  seven  inches  plus  two 
inches,  or  nine  inches,  and  the  weight-arm  seven  inches. 
If,  now,  a  man's  body  weighs,  say,  160  pounds,  which  is 
therefore  the  weight,  how  many  pounds  must  his  tendon 
Achilles  pull  in  order  to  raise  him  on  his  toes?  By  the 
equation  P  X  pa  =  W  X  iva.  Calling  the  power  x  gives  9;r 
=  7X160.  x  =  124%  pounds.  Thus,  by  means  of  this 
arrangement,  to  lift  a  body  of  160  pounds  requires  a  pull  of 
only  124  pounds  at  the  heel. 

Or,  to  take  a  second  example  in  the  case  of  the  fore- 
arm. Suppose  the  distance  from  the  elbow  to  the  point  in 


MUSCLES   AND    PHENOMENA    OF    CONTRACTION.         141 

the  hand  where  the  weight  rests  to  be  fourteen  inches,  and 
the  distance  of  the  point  where  the  biceps  muscle  is  attached 
to  the  radius,  to  be  three  inches  from  the  elbow.  With 
what  power  would  the  biceps  muscle  have  to  contract  to 
raise  fifty  pounds  in  the  hands?  In  this  case  the  power-arm 
is  three  inches  and  the  weight-arm  fourteen  inches.  By 
the  terms  of  the  equation  3  x  =  14  X  50  and  x  =  233l73 
pounds.  In  this  case  much  power  is  lost,  for  to  lift  but 
the  rather  small  weight  of  fifty  pounds  requires  a  pull  of 
233Va  pounds  of  the  biceps,  and  this  on  the  supposition 
that  the  biceps  is  pulling  in  the  most  advantageous  direc- 
tion, while  as  a  matter  of  fact  pulling  at  an  angle  adds  a 
further  disadvantage.  But  while  much  power  is  lost  in  this 
way,  but  a  slight  contraction  of  the  biceps  moves  the  hand 
through  a  much  greater  distance.  By  means  of  these  var- 
ious levers  all  through  the  body  we  are  enabled  to  accom- 
plish the  familiar  movements  of  walking,  running,  jumping, 
swimming,  and  so  on.  The  exact  manner  in  which  these 
various  movements  are  brought  about  may  be  so  easily  de- 
termined by  direct  observation  that  a  full  discussion  of  them 
is  here  omitted. 

The  Hygiene  of  Muscles. 

There  are  but  two  things  in  the  body  which  are  under 
our  immediate  control.  One  of  these  is  the  system  of  vol- 
untary muscles,  and  the  second  is  the  central  nervous  sys- 
tem. These  two  systems  are  placed  in  our  own  hands,  and 
for  the  growth  and  development  of  them,  we  ourselves  are 
directly  responsible,  and  as  on  the  development  of  these 
two  systems  nearly  all  the  other  systems  depend,  we  are 
enabled  in  an  indirect  way  to  be  masters  of  our  whole 
frame.  There  are,  therefore,  but  two  kinds  of  exercise 
under  our  immediate  control — muscular  exercise  and  nerv- 
ous exercise.  Two  kinds  of  education — or,  rather,  two 
phases  of  the  same  education  are,  therefore,  possible,  a 
physical  education  and  the  education  of  the  mind.  No  one 
questions  for  a  moment  that  the  mind,  if  left  to  itself  to 


142  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

shift  as  it  may,  if  never  carefully  directed,  will  ever  become 
properly  developed.  But  we  do  not  yet  seem  to  be  so  clear 
in  reference  to  the  muscular  system.  In  these  days,  when 
intellectuality  is  frequently  made  to  count  so  much  more 
than  health,  the  exercise  of  the  body  is  put  in  the  back- 
ground, in  fact,  lost  sight  of  too  often.  "A  sound  mind  in 
a  sound  body"  is  an  old  maxim,  and  its  validity  is  not 
questioned  by  thoughtful  people.  But  not  only  do  we  want 
a  sound  body  in  order  to  have  a  sound  mind,  we  want  a 
sound  body  for  its  own  sake.  It  is  absolutely  indispensable 
in  those  trades  which  demand  manual  labor  and  physical 
exercise,  and  is  a  necessity  in  intellectual  pursuits  and 
sedentary  occupations.  This  is  evidenced  by  the  number 
of  men  engaged  in  brain  work  who  fall  by  the  wayside 
while  they  are  yet  young.  It  is  illustrated  every  day  in  men 
of  especial  mental  acumen  who  have  their  sun  set  while  it 
is  yet  day.  Exercise  is  the  education  of  the  body,  in  which 
sense  the  term  education  is  identical  with  that  when  ap- 
plied to  the  mind.  Properly  directed  exercise  is  the  fitting 
of  each  part  to  fill  its  place  fully,  and  to  have  it  completely 
adapted  to  the  other  parts.  Exercise  is  not  the  excessive 
or  peculiar  development  of  one  side  or  another,  it  is  the 
all-round  development,  the  result  of  which  is  so  tersely  ex- 
pressed in  that  familiar  word  u  health."  In  olden  times 
exercise  was  made  the  larger  part  of  the  training  of  the 
young  soldier  and  sailor.  Common  experience  has  proved 
that  this  was  an  indispensable  preparation  for  the  taxing  and 
arduous  endurance  of  warfare,  but  they  selected  the  strong, 
the  brave,  the  courageous,  while  the  weak,  the  undeveloped, 
were  neglected  and  pushed  to  the  wall.  In  too  many  ways 
does  this  ancient  notion  still  crop  out  with  us.  How  many 
times  in  our  schools  and  colleges  are  not  the  strong  picked 
out  for  such  training  and  exercise  to  appear  in  competitive 
games,  while  the  weaker  ones  who  need  it  most  are  permitted 
to  sit  in  silence  in  the  grandstand  and  watch  the  sport. 

In  the  physiological  use  of  the  term  exercise,  reference  is 
not    had  to    the    production    of    special    strength   nor  the 


MUSCLES   AND    PHENOMENA   OF   CONTRACTION.         143 

peculiar  training  for  an  especial  exertion,  but  to  that 
rounded  training  that  makes  for  health.  We  all  know  that 
properly  directed  exercise  strengthens  the  muscles,  vitalizes 
the  body  and  increases  its  powers  of  resistance  and  of  work. 
To  the  athlete  such  a  system  of  rigorous  training  is  recog- 
nized by  everybody  to  be  indispensable.  But  not  only  the 
soldier  on  his  marches  or  the  athlete  in  his  contests,  but  the 
minister,  the  teacher,  the  lawyer  and  the  merchant  as  well 
will  later  be  called  upon  to  undergo  as  much  fatigue  and  will 
have  demands  made  upon  their  bodily  strength  no  less  than 
the  former.  The  many  failures  to  meet  these  demands  in 
the  sedentary  vocations  ought  to  be  a  warning.  The  intel- 
lectual professions  are  rilled  with  many  men  who  in  spite  of 
their  sincerest  efforts,  in  spite  of  a  real  enthusiasm  in 
their  work,  drag  themselves  through  their  tasks  with 
languor  and  pain,  weariness  and  discouragement,  and  with 
the  imminent  possibility  of  a  nervous  break-down  always 
hanging  over  their  heads,  when  by  a  properly  exercised 
and  educated  body  they  might  have  been  enabled  to  prose- 
cute their  work  with  pleasure  and  comfort. 

What  accounts  for  this  seeming  neglect  of  our  bodily 
health?  The  principal  reason  is  no  doubt  the  fierce  com- 
petition in  the  field  of  nerve  and  brain.  From  the  nursery 
to  the  college  or  university  the  nervous  strain  goes  on. 
Entrance  tests,  promotions,  appointments  to  scholarships 
or  fellowships,  competitive  examinations,  grades  of  merit, 
late  hours,  weary  reading,  a  slavishness  to  books,  a  strain- 
ing after  facts,  a  crowding  and  cramming,  until  finally  the 
man  is  brought  to  a  halt  in  his  mad  career  by  finding  his 
body  weakening  under  the  protracted  pressure,  and  his 
energies  both  of  mind  and  frame  irreparably  injured.  In 
America  especially  a  premium  is  put  upon  intellectual  pre- 
cocity. Pale,  bookish  children  are  put  on  the  grandstand 
for  exhibition,  to  be  admired  by  parents  and  patrons,  while 
the  ruddy-faced,  broad-shouldered  boy  whose  mind  too  fre- 
quently runs  to  games  and  to  whom  the  attractions  which 
field  and  meadow,  and  wood  and  stream  afford  are  prefer- 


144  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

able  to  the  prosy  text-book,  is  ridiculed  and  classed  as  a 
dullard.  But  in  spite  of  the  praise  showered  upon  the 
former,  it  ought  to  be  an  object  of  our  pity,  while  the  ruddy 
health  and  the  out-door  instincts  of  the  latter  ought  to  be 
things  to  emulate.  This  does  not  mean  at  all  that  the 
training  of  the  mind  ought  to  be  put  into  the  background, 
for  no  less  than  the  muscles  the  mind  needs  its  proper 
amount  of  exercise  to  grow,  but  when  such  mental  exercise, 
especially  in  children,  has  reached  the  point  of  fatigue, 
considerations  of  health  call  for  a  halt  and  invite  attention 
to  the  bodily  wants  of  the  child  in  question. 

Modern  life  has  become  such  a  severe  struggle  for  exist- 
ence that  in  the  battle  all  else  is  lost  sight  of  except  the 
ultimate  goal  desired,  and  so  persons  subject  themselves 
to  greater  and  greater  mental  pressure  in  the  firm  belief 
that  they  cannot  afford  as  a  matter  of  time  and  money  to 
stop  in  their  foolish  expenditure  and  look  after  the  wants 
of  their  mere  bodily  frames.  A  second  reason  is  possibly 
found  in  that  element  of  American  civilization  character- 
ized by  foreigners  as  our  "  hurry."  We  object  to  walking 
when  it  is  possible  to  ride;  we  object  to  doing  anything 
with  our  hands  when  it  may  be  done  more  quickly  in  other 
ways.  To  take  sufficient  time  for  our  meals  seems  fre- 
quently impossible  on  account  of  the  demands  on  our  time 
made  by  our  business,  while  to  break  into  the  hurry  and 
routine  of  the  daily  work  by  taking  a  quiet,  restful  walk  in 
the  open,  fresh  air  an  hour  in  the  morning  and  an  hour  in 
the  evening  seems  entirely  out  of  the  question.  We  act  on 
the  apparent  belief  that  all  of  our  business  is  so  pressing 
that  we  must  jump  on  the  quickest  car  home,  eat  our  dinner 
in  the  most  hurried  way,  make  the  closest  connection  for  a 
car  returning,  and  return  at  the  end  of  such  a  day's  work 
not  earlier  than  supper.  The  third  reason  is  possibly  found 
in  the  fact  that  when  one  becomes  accustomed  to  doing 
without  exercise  there  grows  upon  one  more  and  more  a  dis- 
inclination to  take  it.  In  this  way  exercise  becomes  more 
and  more  a  task,  is  more  and  more  dreaded,  avoided,  and 


MUSCLES    AND    PHENOMENA    OF    CONTRACTION.         145 

the  muscles  on  account  of  their  continued  idleness  become 
more  and  more  weakened,  until  finally  healthy  bodily  exer- 
cise becomes  not  only  a  hardship,  but  an  impossibility. 

No  directions  can  be  given  with  reference  to  the  amount 
of  exercise  to  be  taken.  In  the  case  of  young  children, 
their  love  of  outdoor  games  is  a  natural  solution  to  this 
question.  In  the  case  of  adults,  especially  those  who  are 
engaged  in  sedentary  professions,  at  least  two  or  three  hours 
a  day  ought  to  be  taken  in  good,  invigorating  out-door  ex- 
ercise. If  an  equipped  gymnasium,  such  as  are  becoming 
more  and  more  prevalent,  be  not  available,  the  best  substitute 
is  a  brisk  walk  in  the  open  air.  To  get  the  proper  amount 
of  exercise  for  an  average  individual,  the  walk  of  a  day 
ought  to  amount  at  least  to  three  or  four  miles.  If,  how- 
ever, the  out-door  exercise  may  be  changed  into  some  kind 
of  a  game  which  shall  bring  about  a  mental  relaxation,  as 
well  as  mere  physical  exercise,  much  additional  is  gained, 
for  the  individual  who  walks  along  engrossed  in  his  usual 
train  of  thoughts  loses  the  most  helpful  effects  of. his  ramble. 
There  can  be  no  questioning  of  the  fact  that  the  many 
national  out-door  games  in  England  have  had  very  much  to 
do  in  making  the  English  character,  and  possibly  no  greater 
good  could  befall  this  nation  than  to  have  encouraged  in  it 
a  more  and  more  general  appreciation  of  out-door  sports 
in  which  it  would  be  possible  for  everyone  to  participate. 


CHAPTER  VIII. 


THE  'CIRCULATION. 

In  order  that  the  blood  may  be  of  service  in  the  body  it 
is  necessary  that  it  be  kept  in  circulation.  This  for  two 
reasons:  It  must  bring  new  nourishment  and  new  oxygen 
to  the  part  in  question,  otherwise  the  tissue  would  soon  be 
exhausted,  and  it  must  carry  away  those  products  of  de- 
composition resulting  from  the  activity  of  the  tissues,  other- 
wise these  products  would  accumulate  to  such  an  extent 
as  to  become  poisonous  and  prevent  further  work.  To  ac- 
complish these  purposes  the  entire  amount  of  blood  is  kept 
in  one  constant  whirl,  not  stopping  even  for  an  instant 
throughout  the  entire  life  of  the  individual.  The  stoppage 
of  blood  an  instant  or  two  would  at  once  entail  death. 
And  when  it  is  told  that  a  single  particle  of  blood  is  whirled 
along  at  such  a  speed  that  it  makes  one  complete  circulation 
in  little  more  than  half  a  minute,  passing  in  that  short  in- 
terval twice  through  the  heart,  through  the  capillaries  of 
the  lung  and  over  the  system,  one  may  realize  with  what 
energy  and  rapidity  the  circulation  is  going  on.  The  main 
reason  for  this  speed  is  found  in  the  necessity  for  carrying 
the  oxygen  to  the  tissues  rather  than  the  nutritive  portions 
of  the  blood.  These  nutritive  substances  soak  rather  slowly 
through  the  tissues  in  the  lymph,  while  the  blood  itself,  con- 
fined in  definite  vessels,  is  hurried  along  at  pell-mell  speed 
back  to  the  lungs  to  carry  to  the  tissues  new  quantities  of 
oxygen. 

In  many  of  the  lower  animals  the  necessity  for  a  circu- 
lation is  not  so  great.  Thus  some  of  the  very  tiny  forms  are 
able  to  have  their  nutritive  substances  soak  through  all  parts 
of  their  bodies  by  the  simple  process  of  osmosis,  while  the 
air,  too,  may  be  taken  in  sufficient  quantities  through  the 
(146) 


(Facing  Page  146.    See  Page  155  et  seq.) 

Fig.  74.— THE  ARTERIAL  AND  VENOUS  SYSTEMS  IN  JUXTAPOSITION.     (From  Quain,  after 
Allen  Thomson.) 

The  explanation  of  the  letters  and  numbers  will  be  evident  from  references  to  the 
text  and  to  the  other  figures. 


TH?;    CIRCULATION.  147 

exterior  without  having  special  avenues  set  apart  for  carry- 
ing it.  Then  on  account  of  the  sluggishness  of  many  of 
the  invertebrates,  and  the  further  fact  that  their  bodies 
need  not  be  kept  at  the  relatively  high  temperature  of  warm- 
blooded animals,  their  need  of  a  rapid  circulation  does  not 
exist.  In  such  cases,  as  for  instance  the  clam,  the  blood 
circulates  in  a  much  slower  and  less  perfect  system  than  in 
higher  forms. 

In  the  insects  an  entirely  different  arrangement  is  found. 
The  activity  which  many  of  this  class  exhibit  would  make 
it  imperative  to  have  at  the  disposal  of  their  tissues  abund- 
ant quantities  of  oxygen,  and  if  such  were  to  be  carried  by 
the  blood  from  some  central  lung,  it  would  have  to  run  at  a 
speed  possibly  none  slower  relatively  than  that  found  in  us. 
But  oxygen  in  these  little  active  creatures  is  not  carried  by 
the  blood  directly,  but  is  carried  through  special  vessels  which 
branch  and  re-branch,  carrying  the  air  from  the  exterior  to 
every  part  of  the  body.  In  other  words,  the  insects  have  a 
system  of  air  arteries  and  air  capillaries  permeating  the  en- 
tire body  to  the  minutest  parts,  and  by  this  system  sufficient 
quantities  of  oxygen  are  carried.  The  blood  in  this  case, 
being  relieved  of  its  main  function,  circulates  in  a  very  im- 
perfect way,  and  the  blood  system  is  not  at  all  well  de- 
veloped. 

Simplified  conditions  are  also  met  in  the  lower  forms  of 
vertebrates.  Thus  in  fishes  the  heart  consists  of  but  one 
auricle  and  one  vertricle.  In  the  frogs  and  allied  forms 
there  are  two  auricles,  but  one  ventricle  only,  while,  finally, 
m  the  higher  forms  we  have  four  distinct  cavities  of  the 
heart.  By  this  means  the  blood  reaches  the  heart  twice  in 
one  complete  circulation  instead  of  only  once,  as  in  the 
fishes,  and  is  thus  with  almost  double  energy  forced  on  in 
its  course. 

THE  GENERAL   ARRANGEMENT    OF   THE    CIRCULATORY  SYSTEM. 

To  have  any  liquid  circulate  it  is  necessary  that  at  one 
point  at  least  in  its  course  it  may  be  subjected  to  a  proper 


148  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

power  to  propel  it.  In  every  water- works  system  there 
must  be  at  least  one  central  pumping1  station.  The  central 
station  in  the  circulation  of  the  blood  is,  of  course,  the 
heart.  From  this  arise  vessels  which  lead  the  blood  away 
from  it,  called  arteries.  These  arteries  are  of  two  sets,  one 
carrying  the  impure  blood  to  the  lung,  the  pulmonary  arter- 
ies, the  other  carrying  the  pure  blood  over  the  entire  body, 
the  systemic  arteries.  The  arteries  divide  and  sub-divide 
as  they  proceed,  and  finally  entering  their  respective  tissues 
lead  into  the  plexuses,  or  net-works  of  tiny  capillaries.  In 
these  capillaries  the  walls  are  thin  enough  to  permit  the 
nourishment  held  in  solution  in  the  plasma  to  dialize  through 
and  soak  in  among  the  tissues.  The  oxygen,  too,  in  the 
capillaries  becomes  disassociated  from  the  corpuscles  which 
have  carried  it  to  this  point,  and  along  with  some  of  the 
plasma  which  soaks  through  it  enters  the  lymph  of  the  tis- 
sues. It  will  be  seen,  therefore,  that  in  the  capillaries  the 
arterial  stream,  so  to  speak,  divides,  the  larger  portion  of 
it,  together  with  all  of  the  corpuscles,  remaining  in  the 
capillaries,  and,  being  returned  to  the  heart  through  the 
veins,  while  the  other  part  soaks  through  the  capillary 
walls  and  slowly  and  leisurely  circulates  between,  and  per- 
meates, the  tissues.  This  latter  part  is  designated  as  lymph. 
Lymph,  therefore,  is  but  that  portion  of  the  blood  which  has 
dialized  out  through  the  thin  capillary  walls. 

The  returning  streams,  then,  are  two.  First,  the  veins 
which  carry  the  returning  blood  that  has  not  left  the  capil- 
laries, and  which,  because  they  contain  all  the  red  corpuscles, 
look  red,  and  are  therefore  spoken  of  as  blood  veins;  and 
second,  a  system  of  so-called  veins,  the  lymphatics,  quite 
similar  to  the  ordinary  blood  veins  which  gather  up  the 
lymph  of  the  tissues,  and  finally  through  the  thoracic  duct 
return  this  stream  to  the  original  blood  circulation,  where 
the  thoracic  duct  empties  itself  into  the  left  subclavian  vein. 

THE  ROUTE  OF  ONE  COMPLETE  CIRCULATION. 

Starting  with  a  drop  of  blood  say  in  the  right  ventricle, 
it  is  sent  by  the  contraction  of  this  chamber  through  the 


THE    CIRCULATION.  149 

pulmonary  artery  issuing  from  it,  to  the  lungs.  Here  it 
suffers  changes  which  will  be  discussed  further  on,  the  re- 
sults of  which  are,  that  the  dark  venous  blood  is  changed 
into  the  light  arterial  blood,  which  is  then,  by  means  of  the 
pulmonary  veins,  returned  to  the  left  side  of  the  heart. 
Here  it  flows  into  the  left  auricle,  at  once  proceeds  to  the 
left  ventricle,  and  by  means  of  this  powerful  ventricle  it  is 


Fig.  69. — DIAGRAMMATIC  REPRESENTATION   OF   THE  CIRCULATION   OF   WARM-BLOODED 

ANIMALS. 

o,  auricles;  v,  ventricles;  P,  pulmonary  capillaries;  (7,  systemic  capillaries;  a,  a,  aorta; 
v,  c,  vena,  cava;  a,  p,  v,  p,  pulmonary  artery  and  vein. 

forced  out  through  the  issuing  aorta  and  sent  over  the  body. 
Carried  by  arteries  it  finally  reaches  the  capillaries  of  the 


150 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


tissue  ill  question,  and  after  losing  some  of  its  substance 
into  the  lymph,  it  is  returned  by  means  of  the  veins  to  the 
right  auricle  as  impure  blood,  and  from  the  right  auricle 
proceeds  to  the  right  ventricle,  which  was  its  starting 
point.  It  will  thus  be  seen  that  in  one  complete  circula- 
tion the  blood  passes  through  the  heart  twice,  and  passes 
through  at  least  two  sets  of  capillaries,  those  of  the  lung 
and  the  systemic  capillaries.  It  has  already  been  stated 
that  this  proceeds  with  such  rapidity  that  the  time  required 
for  such  a  complete  circulation  is  but  little  more  than  half 
a  minute. 

THE  HEART. 

1. — Position.  The  energy  to  keep  this  entire  current 
moving  is  furnished  by  the  heart,  which  is  a  large,  muscular 
organ  situated  in  the  chest  extending  from  about  the  second 
to  the  fifth  ribs.  While  it  varies  in  size  under  varying  cir- 
cumstances its  average  size  may  be  roughly  indicated  by 
comparing  it  with  the  double  fists  of  the  person.  It  is 
placed  diagonally  in  the  chest,  with  the  apex  extended 


Fig.  70. — DIAGRAM  TO  SHOW  RELATIVE  POSITION  OF  HEART  IN  THE  CHEST. 

towards  the  left  side  striking  the  chest  wall  in  front,  about 
between  the  fifth  and  sixth   ribs,  while    the  base  extends 


THE    CIRCULATION.  151 

upwards  and  towards  the  right.  As  the  beat  of  the  heart 
may  readily  be  felt  where  the  apex  touches  the  chest,  this 
has  given  rise  to  the  popular  statement  that  the  heart  is  on 
the  left  side.  As  far  as  actual  material  is  concerned,  prob- 
ably as  much  of  it  lies  on  the  right  side  as  on  the  left. 

2. — Coverings.  It  does  not,  however,  hang  loose  in  the 
chest,  but  is  supported  by  a  double  membrane  covering  it, 
called  the  pericardium.  The  heart  does  not  really  lie  inside 
the  pericardium,  although  at  first  appearance  it  seems  to 
do  so.  It  is  entirely  on  the  outside  of  it,  and  the  interior 
of  the  pericardium  is  really  the  space  filled  by  the  peri- 
cardial  fluid  between  the  two  membranes.  If  an  ordinary 
foot-ball  only  loosely  distended  be  pressed  down  over  a  fist 
so  as  to  surround  the  fist,  we  should  have  an  analogous  ex- 
ample. It  is  evident  in  this  case  that  the  fist  is  not  in  the 
collapsed  foot-ball  at  all.  This  pericardium  is  attached  to 
the  walls  of  the  chest,  and  in  this  manner  the  rather  heavy 
heart  is  supported.  The  pericardium  is  really  but  a  con- 
tinuation of  the  pleura. 

3. — Cavities.  As  pointed  out  in  a  previous  chapter,  the 
muscular  tissue  of  which  the  heart  is  composed  is  of  a 
peculiar  kind,  called  the  cardiac  muscle.  This  muscle  is 
thrown  into  such  folds  and  sheets  as  to  form  the  four  cav- 
ities of  the  heart.  Of  these,  the  upper  cavities  are  small, 
and  their  walls  quite  thin.  In  a  cut-out  heart  they  are  usu- 
ally collapsed,  and  look  more  like  little  muscular  append- 
ages than  large  chambers.  On  account  of  their  flap-like 
appearance  they  are  called  "  auricles;"  that  is,  little  ears. 

The  two  lower  cavities  comprise  nearly  all  the  substance 
of  the  heart,  are  entirely  separate  from  the  upper  cavities 
as  seen  from  the  outside,  have  comparatively  very  thick 
walls,  the  left  being  much  the  thicker,  and  are  called  "ven- 
tricles." It  is  the  contraction  of  the  ventricles  that  forces 
the  blood  through  the  arteries. 

4. — Vessels  Arising  from  the  Heart.  A  number  of  ves- 
sels are  connected  with  the  heart,  carrying  blood  to  it  (the 


152 


STUDIKS    IN    ADVANCED    PHYSIOLOGY. 


veins)  and  from  it  (the  arteries).  Into  the  right  auricle 
open  several  large  veins — the  descending  vena  cava,  the  as- 
cending vena  cava,  the  azygos  vein,  and  several  small 


Fig.  71. — VlRW  OF  HEART  AND  GREAT  VESSELS  FROM  BEFORE.      (Quain.) 

3,  pulmonary  artery  cut  off;  1,  arch'of  aorta;  2,  left  ventricle;  4,  aorta;  5,  right  auricle; 
6,  left  auricle;  7,  innominate  veins  joining  to  form  the  descending  vena  cava;  8,  ascending 
vena  cava;  9,  hepatic  veins;  +  +  left  coronary  artery. 

coronary  veins.  The  right  ventricle  is  connected  with  the 
large  pulmonary  artery  leading  to  the  lungs.  The  left 
auricle  has  opening  into  it,  usually  three  or  four  pulmonary 
veins,  while  the  left  ventricle  communicates  with  the  large 
aorta,  which  through  its  many  branches  carries  the  blood 
over  the  entire  system.  From  the  aorta  close  to  the  heart, 
two  arteries  arise  which  lead  through  the  substance  of  the 
heart  itself  and  nourish  it.  These  are  the  coronary  arter- 
ies. A  conspicuous  branch  of  these  coronary  arteries  and 
the  corresponding  returning  coronary  veins,  may  be  easily 


THE    CIRCULATION. 


153 


seen  on  the  exterior  along  the  partition  which  divides  the 
right  and  left  ventricles. 

5. — The  Valves  of  the  Heart.  In  order  that  by  means 
of  the  contractions  the  blood  may  flow  in  the  proper  direc- 
tion, the  heart  is  provided  with  a  series  of  valves,  four  in 
number,  two  between  the  auricles  and  the  ventricles,  one  at 
the  beginning  of  the  pulmonary  artery,  the  fourth  at  the 
beginning  of  the  aorta.  The  valves  below  the  auricles 
are  called  auriculo- ventricular  valves.  The  valve  between 
the  right  and  left  auricle  consists  of  three  flaps  so  arranged 


Fig.  72.— THE  HEART  WITH  SIGHT  AURICLE  AND  RIGHT  VENTRICLE  EXPOSED. 
1,  descending  vena  cava;  2.  ascending  vena  cava;  2',  hepatic  arteries;  3,  3',  3",  walls 
of  auricle;  4,  wall  of  ventricle;  4',  papillary  muscle;  5,5',  5",  tricuspid  valves;  6,  semi- 
lunar  valves;  7,  pulmonary  artery;  8,  aorta;   9,  branches  of  aorta;  10,  left  auricle;  11,  left 
ventricle. 

that  when  they  are  brought  together  they  close  the  opening 
leading  to  the  auricle.     This  is  the  tricuspid  valve.     The 


154  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

valve  between  the  left  auricle  and  left  ventricle  consists  of 
but  two  flaps,  and  is  therefore  called  the  bicuspid,  or,  from 
its  resemblance  to  a  mitre,  the  mitral  valve.  A  rather  rough 
illustration  of  these  valves  may  be  made  by  cutting  say  the 
top  of  an  ordinary  tomato  can  in  such  a  way  that  it  will  be 
divided  into  three  triangular  flaps,  meeting  at  a  point  in  the 
middle  of  the  surface,  somewhat  like  a  pie  cut  into  equal 
thirds.  If  these  parts  of  the  can  were  then  bent  downward 
into  the  can  one  might  easily  see  how  a  liquid  could  be 
poured  into  the  can.  But  if  these  flaps  should  by  the  liquid 
poured  in  them  be  gradually  lifted  up,  until  finally  they 
should  all  meet  again,  and  joining  with  their  edges  fit  per- 
fectly, one  may  see  how  the  return  of  such  water  out  through 
this  opening  would  be  prevented.  Such  is  in  a  general  way 
the  condition  of  things  in  the  heart.  To  prevent  these 
valves  in  the  heart  from  turning  upwards  into  the  auricles, 
they  are  fastened  to  the  walls  of  the  ventricles  by  means  of 
strong  cords  called  the  chordae  tendinae.  Such  cords  do 
not  end,  however,  abruptly  in  the  wall  of  the  ventricle.  If 
such  were  the  case,  these  cords  on  the  contraction  of  the 
ventricles  would  become  slack,  and  so  allow  the  valves  to 
turn  back  into  the  auricles.  To  prevent  the  production  of 
such  slack,  the  cords  run  into  special  muscles  attached  to 
the  ventricular  walls,  which  by  their  contraction  pull  in  the 
slack  on  the  cords  as  rapidly  as  it  is  produced  by  the  ap- 
proximation of  the  ventricular  walls  in  the  heart  beat.  These 
muscles  are  called  the  papillary  muscles. 

At  the  orifice  of  the  pulmonary  artery  and  of  the  aorta 
are  the  semilunar  valves.  These  consist  in  each  case  of 
three  sack-like  flaps  attached  to  the  wall  of  the  issuing  ves- 
sel in  such  a  way  that  when  they  are  distended  with  blood 
they  meet  in  the  center  and  prevent  the  flow  of  blood  past 
them.  These  semilunar  valves  do  not  differ  materially  from 
the  valves  which  occur  regularly  in  veins.  These  valves 
permit  the  blood  to  push  the  flaps  apart  in  entering  the 
vessel,  but  do  not  permit  the  flow  in  the  opposite  direction. 
On  the  middle  of  the  margin  of  each  of  these  flaps  there  is 


a,  occipital  bone;  6,  fifth 
cervical  vertebra ;  c,  d,  c,  first, 
sixth  and  twelfth  rib  respect- 
ively; /,  fifth  lumbar  vertebra. 

I,  superior  vena  cava;    2,  2', 
right  and  left   subclavian 
veins;  3,  right  internal  jugu- 
lar vein;   4,  4',  right  and  left 
external  jugular  veins;   5,  5', 
right  and  left  vertebral  veins ; 
6,  left  subclavian  vein  at  its 
junction  with  the  thoracic 
duct;    7,  7',  8,  mammary  and 
intercostal  veins ;  9,  9,  9,  large 
azygos  vein ;  10,  thoracic  duct ; 

II,  inferior    vena    cava;     12, 
junction  of  azygos  vein  with 
left  renal  vein;  13,  13',  lumbar 
veins    connected    both    with 
azygos  vein  and  vena  cava; 
14,  exteral  iliacs.     (A  portion 
of  the   ascending  vena  cava, 
together    with     the     hepatic 
veins   emptying    into    it,  are 
here  shown  cut  away.) 


14V 


(Facing  Page  155.) 

Fig.  75. — THE  VENA  CAVA  AND  THE  PRINCIPAL  VENOUS  TRUNKS.     (From  Quain,  after 
Allen  Thomson.) 


THE    CIRCULATION.  155 

a  little  cartilaginous  nodule  called  the  nodule  of  Arantius, 
or  corpus  Arantii.  These  may  possibly  serve  to  make  the 
edges  fit  more  perfectly.  The  manner  in  which  these  valves 


Fig.  73. — THE  SEMILUNAR  VALVES  OF  THE  AORTA.     (Allen  Thomson.) 
«,  l>,  c,  the  individual  pouches. 

act  may  be  easily  demonstrated  on  a  beef's  heart  by  open- 
ing the  ventricles  until  the  semilunar  valves  in  question  are 
exposed,  and  then  pouring  water  down  the  pulmonary  artery 
or  the  aorta  toward  the  heart.  In  so  doing  the  semilunar 
pouches  as  distended,  meet  in  the  center,  and  prevent  the 
progress  of  the  liquid. 

THE  DISTRIBUTION  OF  THE  VESSELS  OVER  'THE  BODY. 

1. — The  Arterial  Stream.  It  is  the  aorta  which  springs 
from  the  left  ventricle  of  the  heart  from  which  all  the  sys- 
temic arteries  take  their  origin.  The  first  arteries  branch- 
ing off,  are  the  two  coronary  arteries  of  the  heart,  which 
leave  the  aorta  just  above  the  semilunar  valves.  The  aorta 
then  makes  a  turn  to  the  left,  and  descends  through  the 
chest  and  abdomen.  From  the  arch  of  the  aorta  several  im- 
portant arteries  arise.  The  first  is  the  innominate  artery 
which  at  once  divides  into  the  subclavian,  which  goes  to 
the  arm,  and  into  the  right  common  carotid,  which  goes  to 
the  head.  From  the  right  subclavian  springs  the  intra- 
vertebral  artery  which  goes  to  the  head,  passing  through  the 
intra- vertebral  foramina  of  the  cervical  vertebrae.  The  com- 
mon carotid  divides  into  an  external  carotid  and  an  internal 
carotid,  the  former  going  to  the  face  and  scalp,  the  inner 
to  the  brain.  A  little  to  the  right  of  the  origin  of  the  in- 
nominate artery  the  left  common  carotid  leaves  the  arch  of 
the  aorta.  In  its  branching  and  destination  it  is  the  same 


156  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

as  the  right  common  carotid.  Further  to  the  left  on  the 
arch  of  the  aorta  the  left  subclavian  artery  arises,  going  to 
the  arm.  From  it,  too,  arises  a  left  intra- vertebral  artery 
taking  a  similar  course  on  the  left  side  as  the  corresponding 
one  on  the  right..  The  subclavian  arteries  are  in  each  arm 
continued  as  the  brachial  arteries,  and  at  the  elbow  divide 
into  two  arteries  called  the  radial  and  the  ulnar  arteries.  It 
is  the  right  radial  artery  at  the  wrist  on  which  the  nature  of 
the  pulse  is  usually  determined  by  the  physician.  These  two 
arteries  then  divide  and  in  the  hand  form  the  anastomosing 
branches  which  finally  lead  into  the  ultimate  capillaries. 

Just  below  the  arch  of  the  aorta,  but  still  in  the  chest, 
numerous  small  arteries  take  their  origin,  which  supply  the 
intercostal  muscles.  These  are  called  the  intercostal  arter- 
ies. Lying  a  little  anterior  to  these  in  each  case  are  small 
arteries  going  to  the  lungs,  called  the  bronchial  arteries. 
These  must  not  be  confounded  with  the  pulmonary  arteries 
which  carry  the  blood  to  the  lungs.  The  bronchial  arteries 
carry  arterial  blood,  intended  for  the  nourishment  of  the 
lung,  and  not  sent  to  that  place  to  be  purified. 

At  the  point  where  the  aorta  pierces  the  diaphragm  it 
gives  off  the  artery  for  that  organ  called  the  phrenic  artery. 
Immediately  below  the  diaphragm  a  number  of  important 
arteries  leave  the  aorta  frequently  so  close  together  as  to 
take  a  common  origin.  This  common  origin  or  common 
trunk  is,  when  present,  called  the  cceliac  axis.  Frequently, 
however,  these  arteries  arise,  although  close  together,  still 
separately.  These  arteries  are  the  hepatic  artery,  going  to 
the  liver,  the  splenic  artery  to  the  spleen,  the  gastric  artery 
to  the  stomach,  and  the  pancreatic  artery  to  the  pancreas. 
A  little  further  down  on  the  aorta  the  superior  mesentery 
artery  carries  arterial  blood  to  the  small  intestines.  Then 
follow  the  two  large  renal  arteries,  then  the  spermatic  arter- 
ies going  to  organs  in  the  pelvis,  then  the  somewhat  larger 
inferior  mesenteric  artery  supplying  the  large  intestine,  and 
finally  a  few  lumbar  arteries  supplying  the  body  wall.  At 
this  point  the  abdominal  aorta  divides  into  a  right  and  left 


(Facing  Page  157.) 


Fig.  76. — THE  CIRCULATION  AT  THE  BASE  OF  THE  BRAIN,  THE  CIRCLE  OF  WILLIS.     (From 

Quain,  after  Allen  Thomson.) 

1,  left  internal  carotid  artery;  2,  left  anterior  cerebral  artery;  X,  the  anterior  com- 
municating artery;  3,  left  middle  cerebral  artery,  passing  into  fissure  of  Sylvius,  and 
seen  here  running  over  the  island  of  Reil,  by  the  cutting  away  of  the  left  temporal  lobe; 
4,  left  posterior  communicating  artery;  5,  basilar  artery;  6,  left  posterior  cerebral  artery; 
7,  8,  9,  cerebellar  and  vertebral  arteries. 


THE   CIRCULATION.  157 

common  iliac.  This  in  each  case  divides  into  an  external 
iliac  and  an  internal  iliac.  The  internal  iliac  supplies 
blood  to  the  organs  of  the  pelvis,  while  the  external  iliac 
leaves  the  trunk  and  descends  through  the  thigh  as  the 
femoral  artery.  At  the  knee  it  is  called  the  popliteal  artery, 
which  then  divides  into  the  anterior  and  posterior  tibial 
artery. 

The  arterial  supply  of  the  brain  deserves  special  atten- 
tion. At  the  base  of  the  brain  surrounding  the  optic  tracks 
and  the  pituitary  body  there  is  a  circular  blood  vessel  into 
which  all  the  arteries  that  supply  the  brain  empty.  These 
supplying  arteries  are  the  two  internal  carotids  and  the  two 
intra- vertebral  arteries.  The  two  intra- vertebral  arteries, 
however,  unite  when  they  reach  the  medulla  and  form  the 
basilar  artery  which  runs  from  the  middle  of  the  medulla  to 
reach  the  circular  blood  vessel.  This  circular  blood  vessel 
is  called  the  Circle  of  Willis.  From  it  in  turn  arise  the 
numerous  arteries  which  finally  supply  the  brain.  By  this 
rather  remarkable  arrangement  several  things  are  accom- 
plished. Every  part  of  the  brain  may  receive  blood  brought 
to  it  in  as  many  as  four  different  channels.  Further,  the 
amount  of  the  blood  supply  of  the  brain  will  be  constant 
throughout  its  entire  substance;  and  lastly,  the  pulse  of  the 
carotid  and  intra-vertebral  arteries  is  materially  rediiced  in 
the  Circle  of  Willis,  and  so  the  blood  reaches  the  brain 
largely  relieved  of  these  rhythmic  pulsations. 

THE  VENOUS  SYSTEM. 

The  blood  returns  from  the  head  and  neck  on  each  side 
in  three  vessels  called  the  external  and  internal  jugular 
veins,  and  the  vertebral  vein.  From  the  arm  the  blood  is 
returned  through  the  subclavian  vein.  The  subclavian  veins 
on  each  side  have  emptying  into  them  the  external  jugular, 
then  the  vertebral,  and  then  join  with  the  large  internal 
jugulars  to  form  the  innominate  veins.  There  are  thus  two 
innominate  veins,  although  only  one  innominate  artery. 
The  two  innominate  veins,  after  receiving  several  small 


158  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

veins,  unite  to  form  the  descending  vena  cava.  Into  the 
descending  vena  cava  there  opens  usually  right  close  to  the 
heart  the  large  azygos  vein,  which  brings  the  blood  from 
the  back  body  wall  to  the  heart.  Into  the  right  auricle 
itself  open  several  coronary  veins.  The  blood  is  returned 
from  the  limbs  through  the  external  saphenous  vein  and  the 
internal  crural  vein.  These  unite  on  entering  the  pelvic 
region  into  the  external  iliac  vein,  which  then  joins  with 
the  internal  iliac  vein,  returning  the  blood  from  the  pelvic 
region  to  form  the  right  or  left  common  iliac  vein  as  the 
case  may  be,  which  then  unite  and  form  the  ascending 
vena  cava.  Into  the  ascending  vena  cava  the  large  renal 
veins  pour  the  blood  which  has  just  been  through  the  kid- 
neys, while  close  to  the  heart  several  hepatic  veins  enter 
it,  bringing  the  blood  which  has  just  passed  through  the 
liver.  In  the  lumbar  region  branches  connect  the  ascend- 
ing vena  cava  with  the  azygos  vein,  thus  enabling  blood 
from  that  region  to  reach  the  heart  by  either  of  two  chan- 
nels. 

THE  PULMONARY  CIRCULATION. 

The  circulation  of  the  blood  through  the  lungs  for  pur- 
poses of  purification  is  designated  by  a  special  name,  and 
is  called  the  pulmonary  circulation.  This  consists  of  a 
pulmonary  artery  springing  from  the  right  ventricle  and 
leading  to  the  two  lungs,  and  the  pulmonary  veins,  from 
three  to  five  in  number,  which  bring  the  blood  back  to  the 
left  auricle  after  its  oxygenation  in  the  capillaries  of  the 
lung. 

THE  PORTAL  CIRCULATION. 

In  enumerating  the  veins  which  empty  into  the  ascend- 
ing vena  cava,  one  is  at  first  surprised  that  there  are  no 
veins  from  the  stomach,  spleen,  pancreas,  or  intestines. 
The  blood,  however,  which  has  been  carried  to  these 
organs  is  gathered  up  in  a  special  vein  called  the  portal 
vein,  which  is,  therefore,  of  course,  made  by  the  conjunc- 
tion of  the  gastric  vein,  the  splenic  vein,  the  pancreatic 
vein  and  the  intestinal  veins.  This  portal  vein  carries  all 


(Facing  Page  158.) 
Fig-.  77.— THE  ABDOMINAL  AORTA  AND   ITS  PRINCIPAL  BRANCHES.     (From  Quain,  after 

Allen  Thomson.) 

a,  hyoid  bone;  b,  pneumogastric  nerves;  c,  c,  c,  trachea  and  bronchial  tubes;  d, 
oesophagus;  c,  <?,  lacteals  and  thoracic  duct;  /, /,  azygos  vein;  g,  kidneys;  g' ',  suprarenal 
body;  h,  lumbar  vertebra.  I,  I',  I",  thoracic  aorta;  II,  abdominal  aorta;  1,  coronary  arte- 
ries; 2,  innominate;  3,  left  common  carotid;  4,  left  subclavian;  5,  (on  bronchial  tubes) 
bronchial  arteries;  6,  (on  thoracic  aorta)  oesophageal  arteries;  7,  (in  thorax)  intercostal 
arteries;  8,  (on  abdominal  aorta)  phrenic  artery;  9,  coeliac  axis  with  gastric,  splenic  and 
hepatic  arteries  cut  short;  10,  superior  mesenteric  artery;  at  same  level  the  large  renal 
arteries;  below  10  the  spermatic  arteries;  11,  lumbar  arteries;  below  II  the  inferior  mes- 
enteric artery.  For  explanation  of  figures  in  region  of  neck  see  the  text. 


THK    CIRCULATION.  159 

this  blood  to  the  liver,  where  it  passes  through  the 
capillaries  of  that  organ  before  reaching  the  hepatic  veins 
and  so  returns  to  the  heart. 

It  will  be  observed  that  the  blood  passing  this  way 
passes  in  one  complete  circulation  through  three  sets  of 
capillaries  instead  of  two.  This  circulation  of  blood  through 
the  stomach,  spleen,  pancreas,  intestine  and  liver  is  called 
the  portal  circulation.  The  physiological  reasons  why  the 
blood  from  the  spleen,  stomach,  and  intestines  should  first 
be  sent  to  the  liver  before  being  returned  to  the  heart,  will 
be  discussed  in  detail  in  the  chapter  on  nutrition.  In  an- 
ticipation it  may  be  said  here  that  some  of  the  deepest  phy- 
siological reasons  exist  for  such  a  course. 

THE  HISTOLOGY  OF  ARTERIES,    VEINS  AND  CAPILLARIES. 

Examining  with  the  microscope,  an  artery  is  seen  to 
consist  of  three  coats,  called  the  inner,  the  middle  and  the 
outer  coat.  The  inner  coat  consists  of  a  delicate  membrane 
of  closely  packed  elastic  tissue,  on  the  outside  of  which 
there  is  a  still  more  delicate  serous  membrane  of  flattened 
cells  bound  to  the  elastic  membrane  by  a  finely  fibrillated 
connective  tissue.  The  middle  coat  consists  of  alternating 
layers  of  plain  muscular  tissue,  which  is  usually  arranged 
circularly,  and  layers  of  yellow  elastic  fibers  running  mainly 
longitudinally.  The  outer  coat  is  the  toughest,  and  is 
made  up  mainly  of  closely  felted  bundles  of  white  fibrous 


Fig.  78.— CROSS-SECTION  OF  PORTION  OF  THE  WALL  OF  HUMAN  TIBIAL  ARTERY.     (E.  A.  S.) 
a,  inner  epithelial  coat;  6,  the  elastic  fenestra ted  membrane ;  c,  muscular  layer;  d, 
outer  coat  of  connective  tissue  fibres  mainly. 

tissue.     This  coat  then  gradually  shades  off  into  the  looser 
connective  tissue  in  which  the  artery  is    packed.     These 


160 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


coats  give  to  the  arteries  much  strength  and  elasticity, 
while  the  development  of  the  muscular  coat  makes  contrac- 
tion and  dilatation  possible. 

In  veins  the  inner  and  middle  coat  are  much  reduced, 
but  the  outer  coat  of  strong,  white  fibrous  tissue  is  present. 
For  this  reason  veins  have  much  thinner  walls  and  easily  col- 
lapse when  empty,  and,  of  course,  have  practically  no 
power  of  muscular  contraction  and  dilatation.  However, 
owing  to  the  strength  of  the  outer  coat,  they  are,  neverthe- 
less, not  easily  torn.  With  the  exception  of  the  larger  veins 
near  the  heart,  veins  have  valves  in  their  course.  These 
valves  are  semilunar  folds  fastened  in  such  a  way  as  to  allow 
the  flow  of  blood  towards  the  heart,  but  preventing  it  in  the 


Fig.  79. — VALVES  IN  VEINS. 
a,  laid  open  to  show  pockets;  b,  inner  view  with  valves  closed;  c,  as  seen  from  outside. 

opposite  direction.  These  valves  may  occur  singly,  but  are 
more  often  in  pairs,  while  in  some  instances  three  occur  at 
the  same  point.  By  compressing  the  veins  near  the  wrist 
the  positions  of  the  valves  in  the  congested  portions  may 
be  recognized  by  the  swollen  points  along  the  veins. 

Capillaries  have  all  these  coats  absent,  except  only  the 
innermost  membrane  of  flattened  epithelial  cells.  This  ex- 
treme thinness  of  wall,  it  being  only  one  cell  thick,  permits 
readily  the  phenomena  of  osmosis  and  the  migration  of  the 
white  blood  corpuscles. 

The  boundary  lines  between  arteries  and  capillaries  on 
the  one  hand,  and  capillaries  and  veins  on  the  other,  are 


THE   CIRCULATION.  161 

not  sharp  by  any  means.  The  arteries  as  they  grow  smal- 
ler and  branch  more  and  more,  gradually  lose  the  thickness 
of  their  walls,  until  finally  without  a  single  sudden  break  in 


Fig.  80.— CAPILLARIES  AS  SEEN  IN  THE  WEB  OF  A  FROG'S  FOOT. 

the  transition,  but  the  inner  coat  remains,  when  it  is 
somewhat  arbitrarily  called  a  capillary.  On  the  other  side, 
the  capillaries  have  added  to  them  little  by  little  extra  ele- 
ments in  their  walls,  and  shade  off  without  a  sudden  transi- 
tion here  into  the  veins.  By  the  term  capillary,  therefore, 
is  included  that  small  portion  where  all  the  coats  save  the 
innermost  are  absent,  and  is  more  a  physiological  unit  than 
an  anatomical  one. 

THE  PHENOMENA  OF  THE  HEARTS  BEAT. 

Everybody  is  familiar  with  the  fact  that  throughout  life 
the  activity  of  the  heart  is  shown  in  what  is  familiarly  called 
the  "heart's  beat."  This  beat  may  be  easily  recognized 
in  any  of  three  ways:  First,  where  the  apex  of  the  heart 
touches  the  chest  wall  on  the  front  and  left  side  there  may 
be  felt  at  each  beat  a  little  push  or  jar,  caused  by  the  pres- 
sing of  the  heart  against  this  portion  of  the  chest.  The 
point  at  which  this  is  most  pronounced  is  between  the  fifth 
and  sixth  ribs.  Second,  it  may  be  felt  in  the  pulse  where 
the  beat  of  the  heart  appears  as  a  wave  running  along  the 
larger  arteries  of  the  body.  As  this  is  usually  more  con- 
venient for  observation  the  phenomena  of  the  heart's  beat 
are  usually  studied  in  these  pulsations.  Third,  the  beat  of 
the  heart  may  be  easily  detected  by  the  sounds  which  occur 
11 


162  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

whenever  the  heart  beats.  From  the  fact  that  the  activity 
of  the  heart  was  so  evident,  and  the  further  fact  that  the 
final  evidence  of  death  was  usually  considered  to  be  the 
stopping  of  the  heart,  the  heart  received  an  undue  import- 
ance, traces  of  which  §till  remain  with  us  to  this  day  in 
many  words  derived  from  the  word  "  heart,''  which  we  use 
to  express  courage,  emotions,  vitality,  inner-life,  and  so  on. 
The  finest  qualities  of  persons  we  sometimes  still  designate 
as  the  "  heart"  of  the  man,  when,  of  course,  from  a  scien- 
tific standpoint  the  heart  has  long  been  shown  to  be  nothing 
more  than  a  big  muscular  pump. 

1. — The  rate  of  beat.  The  most  easily  determined 
thing  about  the  heart  beat  is  its  rate.  This  is  in  middle 
adult  life  about  seventy-two  per  minute.  It  is  much  higher 
in  the  foetus,  which  just  before  birth  reaches  140.  From 
this  it  gradually  sinks  through  childhood  until  about  the 
twenty-first  year,  when  the  average  rate  of  seventy-two  is 
reached.  The  rate  is  a  few  beats  slower  in  men  than  in 
women.  L,arge  persons  usually  have  a  slightly  lower  rate 
than  small  persons.  The  actual  rate,  however,  in  anybody 
is  subject  to  great  variation.  These  variations  may  be  owing 
to  temperature,  muscular  exercise,  strong  emotions,  or  be 
consequences  of  fevers  or  administered  drugs. 

2. — The  events  occurring  in  a  single  heart  beat.  Although 
the  time  occurring  between  two  successive  heart  beats  is 
normally  less  than  a  second,  by  means  of  proper  apparatus 
the  individual  events  which  occur  in  a  heart  beat  may  be 
easily  demonstrated.  L,et  us  imagine  the  condition  of  the 
heart  at  the  very  instant  after  a  beat  is  over.  L,et  us  suppose 
that  auricles  and  ventricles  are  empty,  and  the  muscular  sub- 
stance of  the  heart  is  thoroughly  relaxed.  In  this  condition 
the  blood  is  entering  the  auricles,  and  as.  the  auriculo-ventric- 
ular  valves  are  open  the  blood  at  once  falls  through  them  into 
the  ventricles.  The  continued  influx  of  the  blood  through 
the  auricles,  gradually  fills  the  ventricles  and  floats  up  the 
auriculo-ventricular  valves.  Soon  the  point  is  reached 


THE    CIRCULATION.  163 

when  the  ventricles  are  passively  full,  and  the  blood  now 
begins  to  back  up  in  the  auricles.  Dividing  the  time  of  a 
complete  heart  beat  into  ten  periods,  the  time  occupied  in 
this  passive  filling  of  the  heart  occupies  six-tenths  of  the 
complete  time. 

At  this  juncture  the  auricles  begin  to  contract  and  force 
their  added  amount  of  blood  into  the  ventricles,  which, 
being  already  practically  filled  with  blood,  now  become 
gorged  and  distended.  By  this  means  the  auriculo- ventric- 
ular valves  become  tightly  closed.  The  time  required  for 
the  contraction  of  the  auricles  is  about  one-tenth  of  the 
time.  It  is  not  necessary  to  state  here  that  the  two  auricles 
contract  together,  and  the  two  ventricles  together,  as  if 
they  were  in  each  case  but  a  single  structure. 

The  reason  why  the  auriculo-ventricular  valves  are  closed 
by  the  forcing  of  this  extra  blood  into  the  ventricles,  may 
be  explained  by  comparing  the  ventricles  to  a  crowded 
room.  It  is  easily  possible  to  imagine  a  room  so  crowded 
as  to  make  it  impossible  to  open  the  door,  especially  if  the 
crowding  should  be  behind  the  door.  As  soon  as  the  au- 
ricles have  finished  their  contraction  the  ventricles  begin  to 
contract  with  much  greater  force.  Just  at  the  beginning  of 
this  contraction,  when  the  muscles  of  the  ventricles  are 
becoming  taut  and  tense,  the  first  sound  of  the  heart  is 
heard.  Just  how  it  is  produced  will  be  explained  further 
on.  By  the  continued  contraction  of  the  ventricles  the 
blood  is  pressed  harder  and  harder,  until  finally  the  pressure 
is  sufficient  to  open  the  semilunar  valves,  and  the  blood 
flows  into  the  outgoing  vessel.  The  time  required  by  the 
ventricles  in  their  contraction  is  about  three-tenths  of  the 
total  period.  As  soon  as  the  blood  has  been  pressed  into 
the  vessels  the  muscular  fibres  of  the  heart  relax.  The  blood 
in  the  pulmonary  artery  and  aorta,  being  under  consider- 
able pressure,  tends  to  flow  back  into  the  relaxed  heart,  but 
in  so  doing  it  distends  the  semilunar  valves  and  closes 
them.  This  is  the  moment  when  the  second  sound  of  the 
heart  occurs.  This  sound  is  therefore  easily  explained.  It 


164  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

is  but  the  sound  caused  by  the  "slamming  shut"  of  the 
doors  which  lead  from  the  pulmonary  artery  and  aorta  back 
into  the  heart. 

It  will  be  noticed  that  the  heart  in  its  beat  is  at  rest  dur- 
ing a  greater  period  than  it  is  at  work.  The  auricles  work 
but  one  part  in  ten,  the  ventricles  but  three  parts  in  ten, 
while  the  entire  heart  counted  as  a  unit  would  work  but 
four  parts,  and  be  at  complete  rest,  that  is,  passively  re- 
laxed, during  six  parts  of  the  time.  If  the  chest  wall  had 
been  removed  and  the  heart  exposed,  changes  in  its  form 
might  easily  have  been  observed.  During  the  contraction 
the  base  of  the  heart  would  have  changed  somewhat  from 
an  oval  form  to  a  rounded  form,  while  the  apex  would 
have  been  drawn  toward  the  base  and  become  blunter.  A 
material  change  in  the  position  of  the  heart  does  not  occur. 

Such  is,  in  a  general  way,  the  series  of  events  in  one 
beat.  L/et  us  now  turn  to  the  individual  events  in  detail. 

The  Filling  of  the  Heart. 

Each  heart  beat  consists  of  two  periods:  A  period  of 
contraction,  which  is  called  the  systole,  and  a  period  of  re- 
laxation called  the  diastole.  Thus  we  have  an  auricular 
systole  of  one-tenth  and  a  diastole  of  nine-tenths  of  a  beat 
period,  and  a  ventricular  systole  of  three-tenths  and  a  ven- 
tricular diastole  of  seven-tenths.  The  filling  of  the  heart 
falls,  of  course,  in  the  diastole. 

The  question  naturally  arises,  as  the  heart  is  in  a  per- 
fectly relaxed  and  passive  condition,  what  are  the  agencies 
that  propel  the  blood  forward  and  cause  it  to  fill  the  emp- 
tied chambers?  It  was  formerly  supposed  that  the  pressure 
of  the  arterial  blood  behind  the  venous  blood  propelled  this 
backward  to  the  heart.  But  such  a  view  can  easily  be  shown 
to  be  erroneous,  for  when  a  vein  near  to  the  heart  is  opened 
there  is  no  pressure  of  blood  inside  it,  but  there  may  be 
actually  a  tendency  to  a  vacuum,  and  air  be  very  easily 
sucked  in.  This  proves  beyond  question  that  venous  blood 
is  sucked  toward  the  heart  and  not  pushed.  No  doubt  the 


THE   CIRCULATION.  165 

mere  elasticity  of  the  muscular  walls  gives  a  slight  suction, 
much  as  a  sponge  unnaturally  compressed  would  as  soon 
as  the  pressure  was  relieved,  spring  to  its  more  natural 
dimensions.  The  suction  due  to  this  elastic  expansion  of 
the  walls  is,  however,  a  very  small  factor,  and  the  main 
power  of  suction  is  derived  from  the  aspiration  of  the  thorax 
itself.  As  everyone  knows  the  pressure  in  the  thorax  is 
less  than  on  the  outside,  and  a  wound  through  the  chest  wall 
would  at  once  suck  air  into  the  chest. 

In  the  inspiration  the  suction  action  becomes  perfectly 
evident,  and  a  big  stream  of  air  rushes  through  nostrils  and 
mouth  into  the  thorax.  If  the  individual  so  breathing  were 
in  a  medium  of  water,  the  water  would  be  sucked  into  the 
chest  with  the  same  relative  ease  as  air.  But  not  only 
does  the  windpipe  lead  into  the  chest,  but  the  veins  do  also. 
Consequently,  when  the  chest  enlarges  there  is  a  sucking 
action  not  only  upon  the  outside  air  but  also  upon  the  out- 
side blood,  and  the  air  through  the  trachea  and  blood 
through  the  veins  are  sucked  heartwards.  In  very  forced 
expiration  the  condition  of  things  may  be  reversed  and  the 
veins  instead  of  being  sucked  may  be  compressed.  But  even 
in  this  compression  the  blood  is  pushed  on  towards  the  heart 
as  the  valves  in  the  veims  interfere  with  its  backward  flow. 
Thus,  whether  the  veins  are  sucked  or  compressed,  the  re- 
sult is  much  the  same. 

That  the  sucking  action  of  the  chest  has  much  to  do 
with  drawing  the  blood  into  the  heart  is  made  evident  in  the 
filling  of  the  big  veins  and  the  stagnation  of  the  venous 
stream  which  occurs  when  we  hold  our  breath  for  some 
time.  A  person  unable  to  get  his  breath  becomes,  as  we 
say,  black  and  blue  in  the  face.  He  does  so  because  he  is 
no  longer  able  to  suck  the  venous  blood  issuing  from  the 
veins  of  his  skin  into  the  empty  heart.  As,  however, 
the  heart  even  when  the  chest  wall  is  cut  open,  still  has 
venous  blood  flowing  into  it  in  slight  quantities,  it  shows 
that  a  small  amount  of  the  sucking  action  must  be  due  to 
the  elastic  expansion  of  the  heart  itself.  It  is  interesting 


166  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

to  note  in  this  connection  that  the  heart  in  many  of  the 
lower  animals  is  forcibly  expanded  as  well  as  contracted. 
In  the  case  of  the  cray-fish  and  lobster,  for  instance,  large 
muscular  cords  run  from  the  edges  of  the  heart  to  the  body 
wall,  and  by  their  contraction  the  heart  is  forcibly  dis- 
tended. 

During  this  filling  of  the  heart,  as  has  been  stated  be- 
fore, the  blood  does  not  accumulate  in  the  auricle,  but  runs 
unhindered  into  the  ventricle  until  both  ventricle  and  auricle 
are  passively  filled.  At  this  point  the  systole  of  the  auricle 
begins.  The  auricle  does  not  completely  empty  itself,  the 
contraction  probably  going  no  farther  than  the  reduction  of 
the  dimensions  of  the  auricle  to  about  that  of  the  vena 

cava. 

The  Auricular  Contraction. 

The  auricular  contraction  begins  at  the  mouth  of  the  veins 
and  runs  like  a  wave  toward  the  ventricles.  This  explains 
why  the  blood  is  not  forced  back  into  the  veins  rather  than 
into  the  already  filled  ventricle.  As  has  been  stated,  this  time 
occupies  about  one-tenth  of  a  heart-beat  period.  While  the 
auricular  contraction  lasts,  the  on-rushing  blood  of  the  veins 
is  of  course  checked  for  an  instant.  This  slight  checking  of 
the  venous  stream  caused  by  the  inability  of  the  stream  to 
drop  into  the  auricle  during  the  systole  of  that  structure, 
causes  a  slight  pulsation  along  the  veins  known  as  the  venous 
pulse.  This  venous  pulse  is  not  at  all  so  well  marked  as  the  ar- 
terial pulse ,  and  is  due  to  an  entirely  different  thing.  It  starts , 
however,  from  the  mouth  of  the  large  veins  at  the  auricle 
and  runs  along  the  veins  much  like  an  arterial  pulse  along 
arteries.  By  the  contraction  of  the  auricles  the  already 
filled  ventricle  is  forcibly  distended  and  so  enabled  to  throw 
more  blood  out  on  its  systole.  Further,  by  the  pressing  of 
the  blood  into  the  ventricles  the  auriculo-ventricular  valves 
have,  in  a  way  already  described,  been  closed.  At  this 
point,  of  course,  the  systole  of  the  ventricles  begins.  Dur- 
ing this  period  the  auricles  act  as  reservoirs  for  the  entering 
venous  blood  and  in  *Hs  role  they  probably  perform  their 


THE    CIRCULATION.  167 

most  important  function.  Except  for  this  reservoir  in 
which  the  venous  blood  may  temporarily  accumulate  there 
would  have  been  quite  a  marked  stagnation  interfering 
materially  with  the  progress  of  the  venous  stream,  but  by 
this  means  the  blood  flows  on  into  the  heart  uninterruptedly 
while  the  ventricles  are  beating,  and  by  the  time  the  auricles 
are  filled  the  ventricles  have  finished  their  beat,  they  relax 
and  the  accumulated  blood  of  the  auricles  drops  at  once 
into  the  emptied  ventricles. 

The  Contraction  of  the  Ventricles.— Sounds  of  the  Heart. 

At  the  beginning  and  again  at  the  close  of  the  ventricu- 
lar systole  the  familiar  sounds  of  the  heart  occur.  The 
first  sound  is  somewhat  dull  and  represented  by  the  syllable 
('  lubb."  It  was  at  first  supposed  to  be  due  to  the  closing 
of  the  auriculo- ventricular  valves,  but  this  is  not  true. 
These  valves  are  closed  before  the  systole  begins,  and  in 
experiments  these  valves  have  actually  been  pinned  back, 
and  yet  the  sound  occurred.  Still  better  evidence  that  the 
first  sound  is  not  due  to  the  closing  of  these  valves  lies  in 
the  fact  that  when  an  emptied  heart  is  made  to  contract  the 
sound  still  occurs.  While  not  fully  understood,  there  seems 
no  doubt  but  that  this  sound  is  partially  due  to  the  sudden 
tension  of  the  muscular  walls  of  the  ventricles.  The  ven- 
tricular walls  becoming  suddenly  very  much  stretched  and 
taut,  produce  a  series  of  vibrations  which  we  recognize  as 
sound.  A  not  very  close  analogy  may  be  cited  in  the  case 
of  an  ordinary  guitar  string.  If  such  a  string  at  first  hang- 
ing loosely  be  suddenly  as  with  a  jerk  tightened,  it  will  be 
set  into  vibration  and  sound  just  as  if  it  had  been  pulled  by 
the  fingers.  That  this  sound  is  due  to  the  tension  of  the 
muscles  seems  corroborated  by  the  fact  that  the  sound  lasts 
during  the  entire  systole.  That  is,  it  continues  as  long  as 
the  ventricular  walls  are  taut. 

Towards  the  close  of  the  systole  is  heard  the  second 
sound.  This  is  shorter  and  louder,  and  is  plainest  in  the 
regions  of  the  aorta  and  pulmonary  artery.  It  has  been 


168 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


represented  by  the  syllable  "  dupp."  This  sound  is  due  to 
the  sudden  closing  of  the  two  semilunar  valves.  Ordinarily 
the  semilunar  valves  of  the  aorta  and  pulmonary  artery  close 
so  nearly  at  the  same  time  that  the  sound  is  heard  as  one. 
After  violent  exercise,  however,  when  the  pressure  in  the 
aorta  is  materially  increased,  the  semilunar  valves  at  its 
origin  close  perceptibly  sooner  than  those  of  the  pulmonary 
artery,  and  there  are  two  distinct  second  sounds.  The 
earlier  closing  of  the  valves  in  the  aorta  is  due  to  the  greater 
pressure  or  blood  forcing  them  together,  just  as  two  doors 
entirely  alike  would  close  at  different  moments  if  winds  of 
different  strengths  should  strike  them. 

Cardiograms. 

All  these  observations  on  the  events  of  a  heart  beat  may 
be  best  studied  by  means  of  cardiograms.     These  cardio- 


Fig.  81.— CARDIOGRAMS  OF  THE  RIGHT  AURICLK  (R  V)  AND   THE  RIGHT  VENTRICLE 
(E K)  OF  A  HORSE.    THE  DOTTED  LINES  CONNECT  SAME  INSTANTS  OF  TIME. 

grams  are  tracings  made  by  placing  systems  of  levers  on  the 
ventricle  and  auricle,  so  arranged  that  the  systole  of  these 
will  raise  the  levers  and  the  diastole  lower  them.  If,  now, 
the  ends  of  such  moving  levers  be  made  to  trace  a 
line  on  a  plate  moving  past  them  at  a  known  speed,  there 
will  result  curves  such  as  those  pictured  in  figures  81  and  82. 
The  cardiogram  in  figure  82  is  one  made  on  a  pathologic- 
ally exposed  human  heart,  and  so  is  peculiarly  valuable  as 
giving  the  actual  course  of  events  in  man  himself.  In  this 


THE)    CIRCULATION. 


169 


and  in  the  other  figure  the  upper  curve  of  the  cardiogram 
represents  the  events  in  the  auricle,  the  lower  those  in  the 


\ . — - 


Fig.  82.— CARDIOGRAMS  OF  THE  RIGHT  AURICLE  (o  d)  AND  RIGHT  VENTRICLE  (v  d)  TAKEN 

ON  AN  EXPOSED  HUMAN  HEART.      (After  Franck.) 

Vertical  lines  indicate  same  instants  of  time. 

ventricle.     The  two  are  so  arranged  that  vertical  lines  con- 
nect the  same  instants  of  time. 

The  cardiogram  of  the  horse  in  figure  81  was  obtained 
by  pushing  a  tube  provided  with  a  rubber  bulb  at  its  end 
through  the  jugular  vein  in  the  neck  into  the  right  auricle, 
and  a  second  such  tube  through  the  auricle  into  the  ven- 
tricle. The  relative  compressions  of  the  bulbs  in  the  diastole 
and  systole  were  then  recorded  with  a  tambour  and  the 
curves  obtained.  Such  a  tambour  consists  essentially  of  a 
light  metallic  box,  covered  on  one  side  with  a  thin  piece  of 


Fig.  83.— A  TAMBOUR. 
T,  the  metal  box ;  H,  the  recording  lever  resting  on  the  rubber  membrane. 

stretched  rubber.     On  this  rubber  rests  the  recording  lever. 
The  metallic  box  is  connected  with  a  tube  from  the  heart, 


170  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

and  the  slightest  variations  in  pressure  cause  the  rubber, 
and  consequently  the  recording  lever  resting  on  it,  to  move 
up  or  down  as  the  pressure  is  positive  or  negative.  The 
recording  lever  is  then  made  to  write  on  a  suitable  surface 
which  is  moved  along  it.  Rough  cardiograms  may  be  made 
by  connecting  two  tambour  boxes  with  a  rather  inelastic 
tubing,  then  firmly  pressing  one  over  the  point  in  the  chest 
where  the  cardiac  impulse  is  most  perceptible,  and  arrang- 
ing the  other  tambour  for  the  usual  way  of  recording.  The 
pulsations  of  the  chest  wall  caused  by  the  heart  beat  will 
be  transmitted  through  the  system  of  tambours  and  be  re- 
corded on  the  moving  surface.  It  may  not  be  out  of  place 
in  this  connection  to  call  attention  to  the  fact  that  this  car- 
diac impulse  is  not  caused  by  the  chest  wall  being  tapped 
or  struck  by  the  heart.  The  heart  never  leaves  the  chest 
wall,  but  the  impulse  is  caused  by  the  sudden  tension  pro- 
duced at  this  point  when  the  systole  occurs.  Much  as  a 
person  might  produce  an  impulse  on  a  sensitive  surface  by 
first  laying  his  hand  gently  on  the  surface  and  then  sud- 
denly pulling  it  up  into  a  fist  without  removing  it  from  the 
surface. 

On  account  of  the  thick  wall  which  separates  the  tam- 
bour from  the  heart  these  cardiograms  do  not  give  the  finer 


Fig.  84.— THE  POINTS  IN  THE  CARDIOGRAM  OF  THE  VENTRICLE  AT  WHICH  DIFFERENT 

PHYSIOLOGISTS   PLACE   THE   OCCURRENCE   OF   THE   SECOND   SOUND. 

detail  and  are  not  altogether  trustworthy.  In  their  finer 
determination  there  are  still  a  number  of  points  not  yet  per- 
fectly established.  Thus,  observers  have  not  been  able  to 


THE    CIRCULATION.  171 

agree  at  what  point  in  the  ventricular  systole  the  second 
sound  occurs.  In  figure  84  are  given  the  views  of  several 
of  the  leading  physiologists.  It  is  also  an  unsettled  ques- 
tion whether  the  ventricles  completely  empty  themselves, 
or  force  out  only  a  certain  proportion  of  the  contained  blood. 
Evidence  seems  to  point,  however,  to  the  fact  that  the  ven- 
tricles are  practically  emptied  at  each  systole. 

Pathological  Sounds  of  the  Heart. 

In  a  normal  heart  the  auriculo-ventricular  valves  are 
hermetically  closed  and  permit  no  blood  to  flow  back. 
Sometimes,  however,  these  valves  become  deranged  in  some 
way  and  cease  to  close  perfectly,  thus  allowing  at  each  con- 
traction of  the  ventricle  a  slight  regurgitation  of  blood  into 
the  auricle.  The  escape  of  this  blood  through  the  imper- 
fect valves  gives  a  murmuring  sound  easily  detected  by  the 
physician  by  means  of  a  stethoscope,  and  always  an  evi- 
dence that  there  is  a  valvular  insufficiency. 

THE  AMOUNT  OF  BLOOD  FORCED  OUT  FROM  THE  HEART. 

It  has  been  difficult  to  determine  exactly  the  amount  of 
blood  forced  out  from  each  ventricle  at  each  beat.  (It  is, 
of  course,  unnecessary  to  point  out  that  the  average  amount 
must  be  the  same  for  both  ventricles.)  The  amount  of 
blood  which  is  found  in  the  ventricles  of  a  corpse  is  not 
perfectly  reliable,  as  post  mortem  changes  may  have  af- 
fected the  size  of  the  heart.  The  first  experiments  to  de- 
termine this  point  gave  175  to  180  grams  as  the  amount 
sent  out  by  each  ventricle  at  each  systole.  L,ater  experi- 
ments gave  100  grams,  while  more  recently  the  amount  has 
been  put  down  as  low  as  fifty  grams.  Taking  100  grams 
as  probably  not  far  from  the  truth,  it  would  mean  that  in 
one  minute  (seventy-two  beats)  7,200  grams  pass  through 
each  ventricle,  or  in  one  hour  432, 000  grams.  This  is  ap- 
proximately 900  pounds,  or,  expressed  in  fluid  measure,  about 
112  gallons.  In  other  words,  nor  far  from  three  barrels. 
And  as  the  other  ventricle  handles  a  similar  amount,  it 


172  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

means  that  in  the  short  period  of  one  hour,  an  amount  of 
blood  not  far  from  six  barrels  traverses  the  heart. 

THE  ENERGY  WITH  WHICH  THE  HEART  WORKS. 

In  determining  the  actual  work  done  by  anything  it  is 
not  sufficient  to  know  the  amount  of  matter  handled,  but  we 
must  also  know  the  distance  through  which  it  is  lifted. 
Thus,  in  pumping  liquids,  it  requires  just  twice  as  much 
work  to  pump  the  same  amount  of  liquid  twice  as  high. 
The  energy  with  which  the  ventricles  force  out  their  con- 
tained blood  is  not  difficult  to  calculate.  Repeatedly  veri- 
fied experiments  show  that  the  left  ventricle  sends  its  blood 
out  with  such  force,  that  if  there  were  no  friction  it  would 
be  thrown  vertically  upwards  about  a  distance Nof  nine  feet. 
The  force  with  which  the  right  ventricle  throws  out  the 
same  amount  of  blood  is  one-third  as  much,  being  in  this 
case  a  distance  of  only  three  feet.  Or,  to  explain  this  still 
further,  it  means  that  the  left  ventricle  forces  the  blood  out 
with  an  energy  that  would  cause  the  blood  to  rise  nine  feet 
high  in  a  tube,  barring  friction.  Or,  to  re-state  it  again,  it 
means  that  if  there  were  no  friction  in  the  arteries  the  heart 
would  force  blood,  say,  up  to  the  finger  tips  if  the  arms 
should  be  held  vertically  upwards,  even  though  the  distance 
from  the  finger  tips  to  the  heart  were  nine  feet. 

,  Now,  work  is  the  product  of  the  amount  of  matter 
lifted,  and  the  distance  through  which  it  is  lifted.  A  unit 
of  work  is  a  foot-pound.  A  foot-pound  is  the  amount  of 
work  required  to  lift  one  pound  one  foot  high.  Knowing 
the  amount  of  blood  which  each  ventricle  throws  out  and 
the  height  to  which  it  would  be  thrown  if  unhindered,  it  is 
easy  to  determine  the  amount  of  work  the  heart  is  enabled 
to  do  in  definite  periods  of  time.  Thus,  at  every  beat  the 
left  ventricle  throws  out  100  grams,  or  about  3-nr  ounces, 
or  about  .22  pound,  taking  approximate  figures  only.  The 
amount  of  work  is  expressed  by  the  product  of  the  numbers 
giving  the  amount  and  height.  Thus  the  work  of  the  left 
ventricle  for  one  beat  would  be  9X.22;  that  is,  1.98  foot- 


THE   CIRCULATION.  173 

pounds.  For  convenience  sake  let  us  say  two  foot-pounds. 
In  seventy-two  beats  (one  minute)  the  amount  of  work 
would  be  144  foot-pounds.  In  an  hour,  8,640  foot-pounds. 

As  the  right  ventricle  lifts  the  blood  only  one-third  as 
far,  the  amount  of  work  it  does  is  just  one-third  that  of  the 
left  ventricle.  Adding  this  one- third  to  the  amount  of  work 
the  left  ventricle  does  in  an  hour  makes  11,520  foot-pounds. 
Re-stating  that  again,  it  means  that  in  one  hour  the  heart 
has  expended  an  amount  of  energy  that  would  have  lifted 
11,520  pounds  one  foot  high. 

In  the  case  of  a  man  weighing  160  pounds,  it  would  lift 
him  in  one  hour  to  a  distance  of  72  feet,  or  in  one  day  1,728 
feet.  Even  if  the  strong  muscles  of  the  skeleton  should  be 
asked  daily  to  carry  the  body  up  a  mountain  side  to  a  dis- 
tance of  1,728  feet,  it  would  by  no  means  prove  an  easy 
task.  Yet  such  is  the  amount  of  work  the  heart  does  day 
in,  day  out,  without  showing  signs  of  fatigue.  To  state 
this  in  still  another  way — if  the  heart  weighing  300  grams 
should  expend  all  its  energy  in  lifting  itself  only,  it  would 
raise  itself  in  one  hour  to  a  distance  of  13,000  feet.  In 
ability  to  do  work,  the  heart  is  equal  to  -g-J-^-  of  a  horse- 
power. 

THE  INNERVATION  OF  THE  HEART. 

1. — The  Source  of  the  Stimuli.  So  far  the  question 
has  been  ignored,  what  causes  the  heart  to  contract?  Does 
it  beat  in  obedience  to  stimuli  which  reach  it  from  the  out- 
side, like  the  right  arm  in  obedience  to  impulses  from  the 
brain,  or  does  it  beat  by  stimuli  that  originate  within  itself  ? 
This  general  question  can  be  easily  answered  definitely  by 
observing  that  a  frog's  heart  cut  out  of  the  body  will  con- 
tinue under  proper  circumstances  to  beat  for  days,  and  the 
heart  of  a  warm-blooded  animal  will  beat  as  long  as  it  is 
properly  supplied  with  nourishment  and  oxygen.  This 
settles  conclusively  that  the  impulses  to  beat  do  not  reach 
the  heart  from  the  outside,  but  are  intrinsic.  The  question 
then  arises  whether  these  intrinsic  stimuli  are  produced  by 
nerve  centers  within  the  heart  or  by  the  heart  muscle  itself. 


174  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

There  is,  of  course,  considerable  difficulty  in  making  ex- 
tended observations  on  the  heart  of  mammals,  but  it  is  quite 
easy  to  make  such  observations  on  cold-blooded  forms, 
especially  on  the  frog  and  terrapin.  If,  now,  a  frog's  heart 
be  carefully  examined  for  nerves,  two  clumps  of  ganglia 
may  be  found,  one  clump  lying  near  the  opening  of  the 
large  veins,  in  the  so-called  sinus.  These  ganglia  are 
called  after  their  discoverer,  the  ganglia  of  Remak.  The 
second  clump  of  ganglia  lies  in  the  septum  of  the  auricles 
close  to  the  auriculo- ventricular  valves.  These  ganglia  are 
called  the  ganglia  of  Bidders.  The  apex  of  the  ventricle  is 
entirely  free  from  nerve  cells.  As  has  been  stated,  such  a 
heart  properly  treated  will  continue  beating  for  days  with 
its  regular  rhythm.  If,  now,  the  portion  containing  the 
ganglia  of  Remak  be  cut  away  from  the  rest  of  the  heart, 
the  heart  stops  beating  at  once,  while  the  sinus  which  still 
contains  the  ganglia  of  Remak  continues  its  beat  without 
interruption.  This  observation  was  first  made  by  Stannius, 
and  is  still  spoken  of  as  the  experiment  of  Stannius. 

It  would  seem  that  the  only  way  to  explain  this  would 
be  to  assume  that  the  ganglia  of  Remak  are  automatic 
ganglia  which  produce  the  beating,  and  that  the  other 
ganglia  are  stimulated  reflexly  by  these.  For  if  a  heart  so 
severed  from  the  ganglia  of  Remak  be  stimulated  in  some 
mechanical  way  it  will  beat  for  a  while  more  or  less  irregu- 
larly, but  soon  comes  again  to  a  standstill.  This  experi- 
ment then  would  seem  to  be  a  clear  assurance  that  the  beat 
of  the  heart  is  inaugurated  by  the  ganglia  of  Remak,  and 
is  therefore  of  a  purely  nervous  origin.  The  function  of 
the  ganglia  of  Bidders  could  be  explained  by  supposing  that 
they  were  stimulated  by  the  ganglia  of  Remak,  and  so  the 
contraction  carried  into  the  ventricles.  But  there  are  many 
facts  which  will  not  admit  of  such  a  simple  solution  to  the 
problem.  If,  for  instance,  the  apex  of  the  heart,  which  of 
course  contains  no  nerve  cells,  be  cut  off  from  the  rest  of 
the  heart  it  may  be  made  to  beat  regularly.  Here,  of  course, 
is  a  clear  case  that  the  beat  is  not  due  to  nervous  influence. 


THE   CIRCULATION.  175 

Physiologists  have,  therefore,  been  driven  to  the  belief  that 
the  heart  muscle  itself  has  a  kind  of  automaticity  which 
helps  to  produce  the  rhythmic  beat. 

That  these  muscle  cells  themselves  must  be  to  some  ex- 
tent automatic  may  be  further  conclusively  shown  by  cut- 
ting out  a  strip  of  muscle  from  a  terrapin's  heart,  which  has 
no  ganglia  in  it,  and  observing  that  such  a  strip  will  continue 
to  beat  rhythmically  if  it  is  once  started  to  do  so.  Nervous 
influence  is  here  again  entirely  out  of  the  question.  There 
are  still  other  reasons  to  think  that  heart  muscle  is  auto- 
matic and  determines  its  own  rhythm.  Thus,  the  heart  mus- 
cle cannot  be  thrown  into  a  tetanic  contraction,  no  matter 
how  rapid  the  stimuli.  If  the  heart  contracts  at  all  it  will 
beat  with  its  own  rhythm.  Then  again,  the  contraction  of 
the  heart  does  not  vary  with  the  strength  of  the  stimulus. 
A  slight  stimulus  will  not  produce  a  slight  contraction,  and 
a  stronger  stimulus  a  stronger  contraction,  as  in  the  case  of 
all  other  muscles;  but  if  the  stimulus  acts  at  all,  be  it  strong 
or  weak,  it  will  produce  the  natural  rhythmic  beat. 

What  has  been  said  so  far  with  reference  to  the  innerva- 
tion  of  the  heart  has  been  observed  on  the  lower  animals, 
but  there  is  every  reason  to  believe  that  practically  the 
same  conditions  exist  in  the  higher  animals.  By  way  of 
summary  be  it  stated  what  the  condition  of  things  prob 
ably  is  in  the  human  heart.  Near  the  mouths  of  the  veins 
entering  the  auricles  are  groups  of  ganglia  called  here,  also, 
the  ganglia  of  Remak.  A  second  group  of  ganglia  occurs 
in  the  septum  between  the  auricles  at  the  place  where  this 
touches  the  ventricles;  that  is,  in  the  walls  between  the 
two  auriculo- ventricular  valves.  But  unlike  the  frog,  scat- 
tered ganglia  are  found  through  the  apex  of  the  heart.  As 
in  the  case  of  all  animals  where  observations  have  been 
made,  the  impulse  to  beat  in  the  human  heart  is  intrinsic 
and  is  due  probably  to  two  things.  First,  the  ganglia 
themselves  in  the  heart  are  probably  automatic.  Second, 
the  heart  muscles  as  well  possess  an  automaticity,  and  the 
beat  is  the  result  of  these  two  similarly  directed  influences. 


176  STUDIES    IN   ADVANCED   PHYSIOLOGY. 

The  word  1 1  automatic  ' '  has  been  used  a  number  of 
times,  and  a  definition  of  the  meaning  of  this  term  is  im- 
perative in  order  to  understand  what  is  meant  by  saying 
that  both  the  ganglia  of  the  heart  as  well  as  the  muscle 
itself  are  automatic.  Such  a  definition  of  this  term  is  un- 
fortunately not  yet  forthcoming.  Physiologists  are  so  far 
entirely  unable  to  explain  what  it  is  that  causes  the  ganglia 
to  originate  their  nervous  impulses,  or  the  muscle  to  con- 
tract at  definite  periods.  There  is  probably  something 
either  in  the  structure  of  the  heart  or  the  manner  in  which 
it  works  that  excites  the  ganglia  or  the  muscle  substance, 
but  so  far  it  has  been  impossible  to  locate  that.  Thus  the 
term  automatic  is  used  to  designate  a  physiological  con- 
dition of  things,  the  meaning  of  which  we  do  not  yet  have. 

2. — Nerves  reaching  the  heart  from  the  outside.  In 
addition  to  the  intrinsic  nerves  of  the  heart  three  kinds  of 
nerves  reach  it  from  the  outside.  Two  of  these  nerves 
reach  the  heart  from  the  vagus  or  pneumogastric  nerve 
coming  from  the  brain.  The  third  kind  reaches  it  from 
the  sympathetic  system. 

The  fibres  of  the  pneumogastric  which  run  to  the  heart 
are  really  not  fibres  of  the  pneumogastric  at  all ;  they  are 
fibres  of  the  eleventh  pair  of  cranial  nerves  called  the  spinal 
accessory.  A  branch  of  the  spinal  accessory  nerve  unites 
itself  with  the  pneumogastric  and  follows  the  course  of  the 
pneumogastric  through  the  skull  and  the  neck.  If  this 
cardiac  branch  of  the  pneumogastric  be  examined  histo- 
logically  it  is  found  to  consist  of  two  sets  of  fibres,  a  set  of 
small  fibres  and  a  set  of  larger  ones.  Both,  however,  are 
medullated.  On  reaching  the  heart  the  large  fibres  can  be 
traced  into  the  heart,  leading  probably  to  the  intrinsic 
ganglia,  while  the  set  of  small  fibres  seems  to  run  along  the 
surface  of  the  heart  and  loses  itself  in  the  walls  of  the 
ventricles  mainly.  These  smaller  nerves  are  sensory  and 
carry  to  the  brain  the  sensations  of  the  heart. 


THE   CIRCULATION.  177 

Tlic  Pneumogastric  or  Cardio -inhibitory  Nerves. 

The  larger  nerves,  ending  probably  in  the  intrinsic 
ganglia  themselves,  exercise  a  peculiar  and  interesting  con- 
trol over  the  beat  of  the  hear,t.  When  they  are  stimulated 
they  cause  the  beat  to  be  slowed,  and  if  sufficiently  stimu- 
lated may  cause  the  heart  to  stop  beating  altogether.  For 
this  reason  they  are  called  inhibitory  nerves.  When  these 
inhibitory  nerves  by  sufficient  stimulation  cause  the  heart 
to  stand  still  the  heart  stands  still  in  diastole,  perfectly  re- 
laxed, and  not  contracted  in  a  systole.  These  cardio-inhib- 
itory  nerves  not  only  slow  the  rate  of  the  beat,  but  they 
make  the  individual  beats  weaker.  The  result  of  this  ac- 
tion is,  of  course,  to  reduce  the  blood  pressure  in  the  arter- 
ies, because  the  heart  no  longer  forces  the  blood  into  these 
arteries  at  the  accustomed  rate.  These  nerves  seem  to  be 
acting  all  the  time  in  our  bodies  and  thus  continually  keep- 
ing the  rate  of  the  heart  beat  in  check.  For  when  both 
nerves  are  cut  the  heart  at  once  begins  to  beat  faster,  be- 
cause the  inhibitory  action  of  the  vagi  has  been  removed. 

Inhibitory  Center. 

It  is,  of  course,  not  these  nerves  themselves  that  are  in- 
hibitory, for  nerves  are  but  the  avenues  of  impulses  trans- 
mitted to  them.  These  inhibitory  impulses  originate  in  a 
center  which  lies  in  the  medulla,  called  the  cardio-inhibitory 
center.  From  this  center  the  inhibitory  fibres  of  the  vagi 
run  to  the  heart,  and  it  is  of  course  this  center  which  is  in 
a  continual  state  of  excitation  and  so  continually  exercising 
a  checking  control  of  the  heart. 

This  cardio-inhibitory  center  may  be  stimulated  to  in- 
creased action  in  several  ways.  First,  increased  blood 
pressure  in  the  cranium  causes  an  increased  inhibitory 
action.  This  may  be  shown  by  boring  a  little  hole  in  the 
cranium  of  an  animal  and  then  forcing  into  the  cranium 
some  non-irritating  liquid.  A  slowing  of  the  heart  beat  at 
once  follows.  This  also  explains  why  in  apoplexy  the  pulse 
sinks  so  rapidly.  (Apoplexy  is  due  to  the  bursting  of  blood 
12 


178  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

vessels  in  the  brain  and  the  accumulation  of  blood  in 
organ.)  This  may  further  explain  why  a  person  in  lying 
down  usually  has  the  rate  of  his  pulse  lowered,  for  in  the 
lying  posture  the  pressure  of  blood  in  the  brain  is,  of  course, 
suddenly  increased.  The  fact  that  such  an  increase  of  blood 
pressure  should  at  once  by  stimulating  the  cardio-inhibitory 
center  cause  the  heart  to  beat  slower,  is  a  very  fortunate 
circumstance,  for  it  reduces  the  possibility  of  the  rupture  of 
blood  vessels  and  consequent  hemorrhages.  Second,  the 
center  is  further  stimulated  by  psychic  influences.  Strong 
emotions  may  affect  it.  Thus,  fainting,  which  is  usually 
due  to  a  flurry  of  the  emotions,  results  from  a  stoppage  of 
the  heart  caused  by  the  inhibitory  action  of  the  vagi. 
When  this  stoppage  lasts  but  an  instant  no  serious  damage 
results,  but  when  the  inhibition  has  been  so  violent  as  to 
prevent  the  heart  from  resuming  its  beat  for  even  a  little 
while,  death  may  result  for  lack  of  circulation.  The  third 
exciting  cause  is  the  lack  of  oxygen.  If  venous  blood  only 
is  allowed  to  run  through  the  center  the  rate  of  pulse  is 
soon  reduced  and  finally  stops  altogether.  This  is,  of 
course,  the  explanation  of  the  observed  fact  that  in  cases 
of  suffocation  the  pulse  sinks  so  rapidly  and  the  heart  ceases 
to  beat  so  soon.  Fourth,  this  center  may  be  stimulated  by 
afferent  impulses  coming  from  other  sensory  nerves.  A 
severe  blow  on  the  pit  of  the  stomach  may  cause  the  heart 
to  stand  still  for  an  instant.  Here  the  afferent  impulse 
goes  from  the  sensory  nerves  of  the  abdomen  to  the  brain, 
and  there  acts  in  an  exciting  way  on  the  cardio-inhibitory 
center.  Fifth,  in  addition  to  these  impulses  which  affect  the 
center  directly  there  are  a  number  of  drugs  and  poisons 
which  act  upon  the  vagus  nerve  and  so  affect  the  beat  of 
the  heart.  Thus  the  poison  muscarin  stimulates  the  ends 
of  the  vagus  nerve  in  the  heart  and  so  may  bring  the  heart 
to  a  standstill.  The  drug  atropin  lames  the  vagi  and  so 
produces  an  acceleration  in  the  heart  beat,  while  nicotine 
seems  first  to  stimulate  the  nerves  and  so  reduce  the  pulse, 
then  later  to  lame  the  nerves  and  so  by  weakening  the  in- 
hibitory influence  to  increase  the  rate  of  beat. 


THE   CIRCULATION.  179 

The  Depressor  Nerves. 

It  was  pointed  out  previously  that  along  with  these  in- 
hibitory nerves  in  the  pneumogastric  there  reach  the  heart 
along  the  same  avenue  some  sensory  or  afferent  nerves. 
These  instead  of  going  to  the  ganglia  are  probably  distrib- 
uted between  the  muscle  fibres  themselves,  and  carry  to  the 
medulla  sensations  from  the  heart.  Of  course  these  sensa- 
tions very  seldom  reach  consciousness  and  so  we  are  not  aware 
of  them,  but  in  the  medulla  these  afferent  impulses  from 
the  heart  affect  the  centers  and  bring  about  important  phy- 
siological results.  In  a  normal  heart  about  the  only  sensa- 
tion that  might  be  expected  to  come  from  the  heart  would 
be  the  sensation  due  to  too  great  a  pressure  of  blood  in  that 
organ.  Such  afferent  impulses  brought  by  this  nerve  to  the 
medulla  cause  immediate  dilatation  of  arteries  all  over  the 
body,  a  condition  of  things  which  at  once  serves  to  reduce 
the  blood  pressure.  Artificial  experiments  confirm  this  as- 
sertion, for  if  this  nerve  be  cut  and  its  central  end,  that  is 
the  end  connected  with  the  medulla,  stimulated,  a  dilata- 
tion of  the  blood  vessels  over  the  body  occurs  and  the 
blood  pressure  sinks  at  once.  On  account  of  this  action 
this  afferent  nerve  was  called  the  depressor  nerve,  because 
the  result  of  its  impulses  is  to  depress;  that  is,  to  lower  the 
pressure  in  the  arteries.  In  the  rabbit  this  depressor  nerve 
runs  as  a  separate  and  distinct  nerve  to  the  heart,  while  in 
most  animals  and  in  man,  as  already  pointed  out,  it  runs 
along  the  common  pneumogastric  trunk. 

Cardio- accelerator  or  Sympathetic  Nerve. 

In  addition  to  these  two  extrinsic  nerves  a  third  one 
reaches  the  heart.  This  is  a  nerve  which  increases  the  rate 
of  heart  beat  and  is  called  the  cardio-accelerator.  This 
cardio-accelerator  has  its  origin  in  the  medulla  and  spinal 
cord,  also,  but  runs  from  this  through  the  communicating 
branches  to  the  sympathetic  ganglia  lying  in  the  lower 
cervical  and  upper  dorsal  region,  and  from  these  ganglia 
reaches  the  heart.  Passing  as  it  does  from  these  sympa- 


180  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

thetic  ganglia  this  nerve  has  usually  been  called  the  sym- 
pathetic nerve.  When  stimulated  it  not  only  increases  the 
rate  of  the  heart  beat  but  for  a  little  while  also  the  strength 
of  the  individual  beat.  In  its  influence  on  the  heart  it  is 
not  so  pronounced  as  the  vagi,  for  if  at  the  same  instant 
the  vagi  and  the  sympathetic  nerves  be  stimulated  the  rate 
of  the  heart  beat  is  slowed,  showing  that  the  vagi  are  more 
effective.  Just  under  what  circumstances  in  life  these  ac- 
celerator nerves  are  brought  into  play  is  still  not  wholly 
solved.  It  is  probable,  however,  that  the  increase  in  the 
rate  of  pulse  which  follows  muscular  exercise  is  due  to  such 
sympathetic  stimulation. 

The  Accelerator  Center. 

These  accelerator  nerves  come  from  an  accelerator  cen- 
ter which  lies  in  the  medulla,  also.  This  center  is  called 
the  cardio-accelerator  center.  It  is  not  in  a  state  of  con- 
tinuous excitation,  as  in  the  case  of  the  inhibitory  center, 
but  like  the  latter,  it  may  be  excited  by  stimuli  reaching  it 
from  other  sources.  Thus  psychic  influences  such  as 
strong  emotions  usually  increase  the  rate  of  heart  beat, 
familiar  to  everybody  in  the  common  experience  of  having 
"  the  heart  rise  into  one's  throat."  Powerful  stimulation 
of  sensory  nerves  in  general  may  result  in  a  marked  quick- 
ening of  the  heart  beat.  This  quickening  of  the  beat,  of 
course,  at  once  raises  the  arterial  pressure  and  so  enables 
the  animal  to  make  sudden  and  especially  vigorous  efforts. 
This  arrangement  may  be  but  the  attempt  of  nature  to  put 
at  our  disposal  for  sudden  emergencies  an  increased  circu 
lation  to  make  possible  increased  exertions,  and  so  materi- 
ally helD  in  the  preservation  of  our  safety. 

Summary. 

By  way  of  summary  the  innervation  of  the  heart  is 
briefly  re-stated. 

The  beat  of  the  heart  itself  is  due  to  the  automaticity  of 
the  muscular  substance  itself,  and  also  to  the  automatic 


THE    CIRCULATION.  181 

action  to  the  intrinsic  ganglia  of  the  heart.  These  gan- 
glia with  their  nerves  leading  to  the  muscle  cells  inaug- 
urate the  heart  beat.  To  control  this  heart  beat  two  kinds  of 
nerves  reach  it  from  the  exterior:  first,  the  vagi  or  pneumo- 
gastric  nerves,  which  because  they  slow,  and  if  sufficiently 
stimulated,  stop  the  heart  beat,  are  called  cardio-inhibitory 
nerves.  These  are  normally  in  constant  excitation;  and  so 
the  heart  beat  is  always  a  little  slower  than  it  would  of  its 
own  account  be.  Second,  the  sympathetic  or  accelerator 
nerves  reaching  it  by  way  of  the  sympathetic  ganglia,  the 
physiological  action  of  which  is  to  increase  the  rate  of  the 
beat. 

All  these  nerves,  the  intrinsic,  cardio-inhibitory  and  the 
sympathetic,  are  concerned  in  the  movement  of  the  heart. 
They  are  not  sensory.  But  in  addition  to  these  three  motor 
nerves  an  afferent  nerve  reaches  the  heart  carrying  sensa- 
tions to  the  medulla.  This  afferent  nerve,  because  when  it 
is  stimulated  by  conditions  in  the  heart,  it  causes  a  dilatation 
of  the  blood  vessels  in  all  parts  of  the  body,  is  called  the 
depressor  nerve.  The  dilatation  of  the  arteries  everywhere 
is,  of  course,  not  due  to  the  depressor  nerve  itself;  it 
simply  carries  the  afferent  impulse  to  the  medulla,  and  from 
centers  in  the  .medulla  the  impulses  to  dilate  the  arteries 
arise. 

Finally,  it  need  not  here  be  noted  that  these  nerves  are 
in  pairs,  a  pneumogastric  on  each  side  and  a  sympathetic 
right  and  left. 

THE  DYNAMICS  OF  THE  BLOOD  STREAM  IN  THE  VESSELS. 

1. — The  Blood  Pressure.  The  anatomy  and  the  general 
distribution  of  arteries,  veins  and  capillaries  have  already 
been  given;  but  there  still  remains  the  discussion  of  the 
phenomena  of  the  blood  in  motion.  By  the  beat  of  the  heart 
the  blood  is  thrown  into  the  arteries,  where  it  accumulates 
until  it  reaches  a  certain  pressure  sufficient  to  force  it  out 
through  the  small  capillaries  at  the  peripheral  ends.  The 
most  apparent  observation  probably  in  examining  an  artery 


182  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

would  be  the  fact  that  the  artery  seems  to  be  distended, 
and  the  blood  in  it  under  considerable  pressure.  This 
pressure  is,  of  course,  produced  by  the  resistance  offered  to 
the  flow  of  blood  through  the  small  arteries  and  capillaries 
on  the  one  end  and  the  continued  pouring  in  of  blood  by 
the  heart  at  the  other  end.  The  condition  of  things  differs 
in  no  way  from  that  of  a  city  water- works  system.  In  that 
case  the  central  pump  usually  forces  the  water  into  the 
mains  at  such  a  rate  that  often  a  heavy  pressure  results. 
Especially  so  in  cases  of  fire  when  the  central  pumps  are 
made  to  run  faster  than  usual.  If  there  were  no  resistance 
at  the  farther  ends  of  these  water  mains,  no  pressure  would 
arise,  but  the  water  would  flow  out  at  one  end  as  rapidly  as 
it  entered  at  the  other.  But  the  pressure  in  the  mains  re- 
sults from  the  internal  resistance  due  to  friction  given  to 
the  stream  as  it  tries  to  traverse  the  smaller  pipes  at  the 
distal  extremity.  In  such  a  system  with  the  pump  going  at 
a  regular  rate  the  pressure  in  the  mains  would  rise  and  rise 
until  finally  a  pressure  would  result  which  would  be  able  to 
force  out  at  its  peripheral  end  as  much  water  in  a  given 
time  as  the  pump  poured  into  it  at  the  other  end.  Thus, 
in  such  a  system,  if  in  a  case  of  fire  the  central  pump  should 
increase  its  speed  the  pressure  throughout  all  the  mains 
would  at  once  rise,  and  continue  to  do  so  until  it  would  be 
able  to  force  through  all  the  finer  ramifications  as  much 
water  as  entered.  It  is  easy  to  determine  what  the  amount 
of  this  pressure  is  in  the  case  of  the  blood-vessels.  From 
general  considerations  which  govern  the  supply  of  all  streams 
flowing  in  closed  tubes,  the  pressure  must  be  greatest  near- 
est the  heart  and  become  gradually  less  towards  the  peri- 
phery. Just  as  in  water  mains  the  pressure  is  greater  near 
the  station  and  gradually  decreases  toward  more  distant 
places. 

Arterial  Pressure. 

The   blood   pressure   in   the   human   arteries    has    been 
measured  in  cases  of  amputation.    Experiments  of  this  kind 


THE    CIRCULATION.  183 

in  the  case  of  the  femoral  artery  showed  a  pressure  of  about 
120  millimetres,  or  about  5  inches  of  mercury.  Experi- 
ments on  tibial  arteries  made  the  pressure  higher,  results 
indicating  here  160  millimetres,  or  about  6|  inches  of 
mercury,  while  the  average  pressure  indicated  by  a  sphyg- 
mometer  (an  instrument  which  may  be  used  on  an  artery 
without  injuring  it),  reaches  about  180  millimetres,  or  7 
inches  of  mercury,  in  the  case  of  the  radial  artery.  As  the 
pressure  in  the  aorta  must  be  somewhat  greater  than  in  any 
of  these  arteries,  it  is  probably  not  far  from  200  millimetres, 
or  8  inches  of  mercury. 

To  more  fully  understand  what  is  meant  by  a  pressure 
of  eight  inches  of  mercury,  comparison  may  be  made  with 
the  barometer.  Here  the  pressure  of  the  air  is  also  meas- 
ured by  a  column  of  mercury.  As  every  one  knows,  the 
air  pressure  supports  about  thirty  inches  of  mercury.  As 
the  atmospheric  pressure  to  the  square  inch  is  about  fifteen 
pounds  it  means  that  every  two  inches  of  mercury  indicate 
one  pound  of  pressure  to  the  square  inch.  Thus,  therefore, 
an  arterial  pressure  of  eight  inches  of  mercury  means  a 
pressure  against  every  square  inch  of  arterial  wall  of  four 
pounds.  As  mercury  is  a  little  over  thirteen  times  heavier 
than  water  or  blood,  it  means  that  the  arterial  pressure 
would  lift  a  column  of  blood  or  water  thirteen  times  eight 
inches,  or  not  far  from  nine  feet.  To  state  the  same  thing 
in  still  another  way,  it  means  that,  disregarding  friction, 
blood  would  spurt  from  such  an  artery  at  such  a  pressure 
vertically  upward,  nine  feet. 

In  the  pulmonary  artery  the  pressure  is  only  about  one- 
third  of  that  in  the  aorta.  This  relatively  low  pressure  in 
the  pulmonary  system  is,  of  course,  equally  easily  explained 
when  we  recall  that  the  blood  traverses  a  much  shorter 
distance,  and  that  the  lung  capillaries  are  more  easily 
traversed. 

Pressure  in  Capillaries. 

The  arterial  pressure  sinks  rapidly  in  the  smaller  arteries 
and  in  the  capillaries  is  very  slight  indeed.  There  are 


184  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

especial  reasons  why  this  ought  to  be  so.  The  capillary 
walls  are  exceedingly  thin  and  would  not  be  able  to  with- 
stand any  material  pressure,  but  would  be  easily  ruptured 
and  so  disastrous  hemorrhages  ensue. 

Pressure  in  Veins. 

The  pressure  in  the  large  veins  is  usually  negative,  that 
is  to  say,  there  is  an  actual  sucking  action.  The  blood  in 
the  veins  is  not  pushed  towards  the  heart  from  behind,  but 
is  sucked  up  towards  the  heart  by  the  aspiratory  action  of 
the  chest,  especially  in  inspiration.  If  by  holding  the 
breath  the  blood  be  allowed  to  accumulate  in  the  veins, 
there  may  be  produced  a  temporary  venous  pressure,  espe- 
cially if  by  active  muscular  exertion  the  smaller  veins  be 
compressed  and  so  the  blood  forced  towards  the  heart.  But 
under  normal  conditions  it  seldom  reaches  a  pressure  of 
more  than  three  to  five  millimetres  of  mercury,  a  very  slight 
one  compared  with  the  high  arterial  pressure. 

Variation  in  Arterial  Pressure. 

The  arterial  pressure  is,  of  course,  immediately  influ- 
enced by  the  rate  of  the  heart  beat.  If  the  heart  beats 
faster,  the  pressure  rises;  if  slower,  it  sinks.  Thus,  in 
cases  of  excitement,  when  the  heart  beats  fast,  the  in- 
creased pressure  resulting  therefrom  not  infrequently  leads 
to  the  bursting  of  blood-vessels  and  apoplexy.  Normally 
when  as  a  result  of  increased  muscular  effort  the  heart  is 
made  to  beat  faster,  general  experience  testifies  to  an  in- 
creased arterial  pressure. 

In  the  second  place  the  arterial  pressure  may  be  varied 
by  the  contraction  or  dilatation  of  the  peripheral  arteries. 
It  will  be  remembered  that  the  arteries  especially  were  pro- 
vided with  a  coat  of  plain  muscular  tissue.  This  coat  is 
under  nervous  control,  and  by  it  the  arteries  are  enabled  to 
contract  their  lumen  or  to  dilate  it.  It  is,  of  course,  at 
once  apparent  that  a  contraction  of  the  small  blood-vessels 
increases  the  arterial  pressure  in  the  same  way  that  closing 


THE    CIRCULATION.  185 

the  nozzle  of  a  hose  at  once  increases  the  pressure  of  the 
water  in  it.  In  fact,  the  explanation  of  such  a  common 
thing  as  a  cold  is  found  in  the  fact  that,  due  to  a  compres- 
sion of  the  vessels  of  the  skin,  caused  as  a  rule  by  an 
exposure  to  suddenly  lowered  temperatures,  an  increased 
arterial  pressure  results  and  the  blood  is  driven  in  undue 
amounts  through  the  vessels  of  the  interior  organs  which 
are  thereby  congested  and  an  inflammation  results  which  we 
designate  as  a  cold. 

In  the  third  place,  there  is  a  slight  variation  produced 
by  the  rhythmic  beat  of  the  heart.  It  is  easily  understood 
how  the  sudden  injection  of  a  ventricle  full  of  blood  into 
the  arteries  will  cause  the  pressure  in  them  to  rise  a  little, 
while  during  the  diastole  of  the  heart  as  the  blood  is  con- 
tinually flowing  out  into  the  capillaries  the  pressure  tends 
to  sink  a  little.  This  variation  is,  however,  very  slight, 
amounting  to  little  more  than  a  few  millimetres  of  mercury. 
As  the  average  pressure  of  the  aorta  is  as  much  as  200  mil- 
limetres of  mercury,  the  periodic  rise  and  fall  of  but  a  few 
millimetres  causes  practically  no  effect. 

THE  CHANGING  OF  THE  INTERMITTENT  FLOW  FROM  THE  HEART 
INTO  THE  CONSTANT  FLOW  OF  THE  CAPILLARIES. 

If  capillaries  like  those  in  a  frog's  foot  be  examined  and 
the  blood  be  seen  circulating  through  them,  it  may  be 
noticed  that  the  blood  flows  smoothly  and  regularly,  show- 
ing no  pulsations.  Even  through  the  smaller  arteries  the 
blood  stream  seems  to  all  external  appearances  to  be  per- 
fectly constant  and  regular.  As  the  blood  is,  however, 
poured  into  the  arteries  by  the  heart  in  periodic  pulsations 
the  question  arises,  how  such  an  intermittent  flow  is  changed 
into  a  regular  and  continuous  one.  This  is  readily  ex- 
plained if  it  be  remembered  that  the  real  force  which  drives 
the  blood  from  the  arteries  into  the  capillaries  is  the  force 
exerted  by  the  elastic  walls  of  the  arteries  which  are  much 
distended  and  which  in  trying  to  regain  their  original  di- 
mensions press  upon  the  contained  blood.  Much  as  water 


186  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

may  be  compressed  by  forcing  it  into  a  hose  of  very  elastic 
rubber  and  then  closing  both  ends.  If  slight  openings  into 
such  a  distended  rubber  hose  would  be  made,  the  water 
would  at  once  be  forced  out  by  the  elasticity  of  the  walls. 
The  pressure  of  the  blood,  which,  of  course,  is  but  the 
amount  of  compression  due  to  the  elastic  walls,  is,  as  has 
been  stated,  200  millimetres  of  mercury,  or  four  pounds  to 
the  square  inch  (in  the  aorta) .  It  is  this  pressure  which 
forces  the  blood  onward.  Even  when  the  heart  is  not 
beating  at  all,  the  pressure  still  continues  in  the  vessels 
keeping  the  stream  in  motion.  When  the  heart  throws  in 
its  amount  of  blood  at  each  beat  this  arterial  pressure  is 
raised  but  very  little,  only  three  to  four  millimetres.  Such 
a  slight  change  in  the  pressure  would  not  affect  the  flow 
through  the  capillaries  at  all,  any  more  than  the  fluctuation 
of  a  few  pounds  of  pressure  in  the  central  pump  of  a  water- 
works station  could  be  detected  by  the  individual  who  is 
watching  the  stream  issue  from  the  nozzle  of  his  hose  in  a 
distant  section  of  the  city. 

THE  RATE  AND  TIME  OF  THE  BLOOD  FLOW. 

1. — Rate.  The  rate  at  which  the  blood  moves  forward  in 
these  vessels  varies  at  different  points  along  its  course.  It 
is  fastest  near  the  heart  and  becomes  gradually  slower  towards 
the  peripheral  ramifications.  This  different  rate  of  flow,  is, 
of  course,  compensated  by  the  fact  that  the  combined  lumen 
of  the  arteries  and  veins  becomes  gradually  larger  as  we  ap- 
proach the  periphery.  This  is  easily  understood  by  watch- 
ing the  flow  of  water  in  a  river.  Where  the  river  is  wide  the 
flow  is  sluggish,  but  where  the  banks  of  the  river  approxi- 
mate each  other  the  river  may  have  quite  a  swift  current. 
Thus,  the  forward  motion  of  the  water  on  Lake  Erie  is  prob- 
ably not  perceptible,  but  when  the  forward  flow  of  the  lake 
becomes  narrowed  between  the  banks  of  the  Niagara  River  it 
may  be  changed  into  a  torrent.  The  fact  that  the  blood  does 
not  flow  as  rapidly  in  the  veins  as  it  does  in  the  arteries  is  due 
to  the  same  thing,  the  veins  being  correspondingly  larger. 


THE    CIRCULATION.  187 

While  it  lias  been  impossible  to  measure  the  exact  rate 
of  flow  in  the  vessels  in  man,  repeated  experiments  have 
been  made  on  the  lower  animals,  and  certain  inferences 
have  been  drawn  from  them  with  reference  to  the  condition 
of  things  in  the  human  body,  which  are  probably  not  very 
far  from  the  truth.  Such  calculations  show  that  the  blood 
in  the  human  carotid  flows  about  400  millimetres,  or  six- 
teen inches  in  a  second.  In  the  smaller  arteries  it  is,  of 
course,  less,  while  finally  in  the  narrow  capillaries  the  blood 
moves  through  a  distance  of  about  -gV  of  an  inch  only  in  a 
second.  As  capillaries  in  a  very  general  way  are  about  -§V 
of  an  inch  long,  it  means  that  it  takes  the  blood  about  one 
second  to  traverse  them.  In  the  larger  veins  the  rate 
is  from  100  to  125  millimetres,  that  is,  from  four  to  five 
inches  per  second.  This  rate  may  be  much  modified  by 
variations  in  the  energy  of  the  respiratory  movements.  As 
in  the  case  of  the  smaller  arteries,  so  with  the  smaller 
veins,  the  rate  is  much  slower  than  four  inches. 

2. — Time.  These  measurements  of  the  rapidity  of  the  flow 
have  been  made  on  the  lower  animals  by  interpolating  be- 
tween the  cut  ends  of  the  vessel  some  form  of  bent  glass 
tube  through  which  the  gradual  streaming  of  the  blood  could 
be  visible  throughout.  As  the  rate  of  flow  is  different  for 
nearly  all  portions  in  the  course,  it  is  impossible  by  this 
means  to  calculate  how  much  time  would  be  required  for 
the  blood  to  make  its  round  through  lung  or  tissues.  It  is, 
however,  possible  to  make  such  determination  and  to  dis- 
cover very  accurately  the  exact  amount  of  time  it  takes  a 
drop  of  blood  to  pass  through  the  routes  of  circulation. 
Thus,  if  some  substance  which  could  easily  be  detected  be 
injected  into  the  carotid  artery  of  a  horse  and  the  re-appear- 
ance of  such  injected  substance  watched  for  in  the  blood 
returning  from  the  jugular  veins,  the  time  to  traverse  the 
circulation  between  these  two  points  would  be  at  once 
given.  Experiments  of  this  kind  on  lower  animals  and  cal- 
culations from  these  to  the  human  body  show  that  on  an 
average  the  time  required  for  the  blood  to  make  one  com- 


188  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

plete  circulation  is  about  thirty-two  seconds.  Of  this  time 
about  nine  seconds  are  lost  in  passing  through  the  pul- 
monary circulation,  the  other  twenty-three  through  the 
systemic . 

The  real  rapidity  with  which  the  blood  moves  may, 
therefore,  be  readily  appreciated  from  this  when  we  remem- 
ber that  a  corpuscle  of  blood  might  in  the  course  of  such  a 
short  time  as  one  hour  carry  120  loads  of  oxygen  to  the 
head.  It  means  that  the  entire  amount  of  blood  in  the  body 
is  moved  in  a  period  of  time  no  greater  than  one  minute 
twice  over  the  entire  course  of  circulation.  If  one  should 
fancifully  try  to  calculate  how  many  loads  of  oxygen  on  an 
average  a  red  corpuscle  would  carry  in  the  course  of  a 
month,  the  figures  would  no  longer  be  comprehensible; 
while  if  the  calculation  should  be  extended  in  computing 
the  actual  distance  which  such  a  corpuscle  had  covered  in 
this  vast  number  of  trips  the  result  might  possibly  be  com- 
prehended only  when  reduced  to  miles. 

In  this  connection  it  may  be  well  to  repeat  that  this 
whirl  of  blood  is  mainly  for  the  purpose  of  carrying  in  an 
uninterrupted  flow  the  supply  of  oxygen  to  all  parts  of  the 
body,  and  only  incidentally  to  carry  the  nourishment  and  to 
remove  the  waste,  even  though  these  two  latter  are,  of 
course,  indispensable. 

THE  PULSE. 

1. — Cause  of  Pulse.  The  sudden  injection  of  several 
ounces  of  blood  at  each  beat  into  the  aorta  causes  the  walls 
of  the  aorta  to  be  additionally  distended  right  at  the  heart 
in  order  to  make  room  for  this  new  amount.  This  expan- 
sion at  the  origin  of  the  aorta  is  made  possible  by  the  elas- 
ticity of  its  wall.  But  by  this  elasticity  the  walls,  distended 
so  suddenly,  try  to  regain  their  original  position,  and  in  so 
doing  start  a  wave  along  the  artery  familiar  to  us  all  as  the 
pulse,  much  like  a  pebble  thrown  into  the  water  will  start 
at  that  point  a  series  of  waves  running  in  every  direction. 
Of  course  in  the  case  of  the  aorta,  the  only  direction  possi- 
ble is  toward  the  periphery. 


THE    CIRCULATION .  189 

2. — Rate  of  Speed  of  Pulse.  This  wave  runs  at  a  defin- 
ite speed  along  the  arteries,  which  is  in  man  about  twenty- 
five  or  thirty  feet  per  second.  This  rate  shows  that  a  pulse 
wave  runs  out  at  its  peripheral  end  and  is  over  before  the 
succeeding  one  is  inaugurated.  This  wave  must  not  be 
understood  as  an  actual  forward  movement  of  the  blood, 
but  is  a  mere  pressure  wave,  just  as  in  the  motion  of  waves 
on  a  surface  of  water,  the  water  itself  does  not  move  for- 
ward with  the  waves,  but  moves  up  and  down  in  almost  the 
same  place,  as  is  indicated  by  observing  any  floating  object 
which  does  not  travel  along  with  the  wave  at  all. 

3. — Kinds  of  Pulses.  An  examination  of  the  pulse  wave 
enables  the  practiced  physician  to  learn  much  about  the 
state  of  things  in  the  general  circulation.  Thus,  a  phy- 
sician can  distinguish  four  different  kinds  of  pulses:  First, 
\kzpulsusfrequens,  or  the  pulsus  rarus,  depending  on  the 
number  of  heart  beats  per  minute.  Second,  the  pulsus 
celer,  or  the  pulsus  tardus,  depending  on  the  quickness 
with  which  a  single  beat  is  t  accomplished.  It  indicates 
whether  in  the  individual  beat  of  the  heart  the  ventricles 
contract  energetically  or  slowly.  This  must  not  be  con- 
founded with  the  rate  of  the  pulse  or  \hz  pulsus  frequens ,  for 
the  heart  might  beat  but  fifty  times  a  minute,  say,  a  very 
slow  rate,  and  yet  perform  each  beat  with  a  quick,  jerky 
systole.  Third,  t\\e  pulsus  magnus,  or  the  pulsus  parvus, 
depending  on  the  amount  of  blood  which  is  thrown  into  the 
arteries  at  each  beat.  A  pulsus  magmis,  or  big  pulse, 
would  be  indicated  by  the  increased  size  of  the  artery  in 
question,  while  a  pulsus  parvus,  or  small  pulse,  would  be 
indicated  by  a  more  or  less  collapsed  artery.  Fourth,  the 
pulsus  durus,  or  the  pulsus  mollis,  that  is,  a  hard  pulse  or 
a  soft  pulse,  depending  on  the  amount  of  pressure  necessary 
to  completely  compress  an  artery,  and  so  prevent  the  blood 
from  flowing  past  the  point  of  compression.  In  other  words, 
the  pulse  is  hard  when  the  pressure  of  blood  is  high  and 
vice  versa.  Here,  also,  a  hard  pulse  must  not  be  con- 
founded with  a  big  pulse.  Thus  it  is  possible  to  conceive 


190  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

a  condition  of  things  in  which  a  greatly  increased  peri- 
pheral resistance  in  the  arteries  should  arise  and  produce  a 
hard  pulse,  and  yet  the  heart  itself  might  force  but  a  small 
amount  of  blood  into  the  artery  at  each  beat  and  so  indicate 
a  small  pulse  at  the  same  time. 

4. — Physiological  Measurements  of  the  Pulse  and  Ar- 
terial Pressure  in  General.  Every  one  knows  that  the  pres- 
sure in  the  arteries  may  be  easily  determined  by  feeling  it 
with  the  finger.  The  rhythmic  variation  in  arterial  pres- 
sure which  we  call  the  pulse,  is  commonly  examined  in  this 
way.  But  in  order  to  show  with  much  finer  detail  all  the 
phenomena  of  arterial  pressure,  various  forms  of  sensitive 
instruments  have  been  devised.  Possibly  the  most  satis- 
factory one  is  the  sphygmograph.  This  consists  essentially 
of  a  sensitive  recording  lever  placed  on  the  artery  in  such  a 
way  that  any  increase  in  the  pressure  of  the  artery  will  raise 
the  lever.  The  lever  itself  is  then  arranged  to  write  on 
some  suitable  moving  surface  and  so  a  curve  of  pressure  is 
obtained.  The  philosophy  of  such  an  instrument  is  almost 
too  simple  to  need  further  explanation.  Every  one  knows 
that  by  putting  the  finger  on  the  pulse  we  feel  the  wall  of 
the  artery  rise.  In  fact,  this  rising  we  called  the  pulse.  If, 
now,  instead  of  the  finger  a  sensitive  lever  be  placed  on  the 
artery,  it  is,  of  course,  easy  to  see  that  at  the  moment  the 
pulse  wave  is  under  the  lever  it  will  lift  the  lever,  and  if 
the  distal  end  of  the  lever  is  provided  with  a  recording  point 


Fig.  85. — SPHYGMOGRAPHIC  CITRVKS,  i  KOM  HTM  AN  KADIAI.  AUTKRY. 

a  curve  will  be  the  result.  The  sphygmograph  possesses 
the  great  advantage  that  it  can  be  used  easily  and  without 
any  injury  to  the  blood  vessels,  and  so  is  adapted  for  the 


THE    CIRCULATION.  191 

study  of  the  pulse  of  man  himself.    In  Figure  85  there  are 
indicated  such  sphygmograph  curves. 

On  animals  there  is  more  generally  used  an  instrument 
called  the  kymograph.  This  is  in  principle  a  revolving 
drum  run  by  clockwork  on  which  the  recording  lever  traces 
the  desired  curves.  This  lever  rests  on  the  mercury  in  one 
limb  of  a  U-shaped  tube,  while  the  other  limb  of  this  U- 
shaped  tube  (D  in  Figure  86)  is  directly  connected  with  the 
cut  end  of  the  artery  to  be  examined.  To  prevent  the 
blood  from  touching  the  mercury  there  is  put  over  it  in  that 
part  of  the  tube  some  liquid  which  will  prevent  the  blood 
from  clotting.  Upon  connection  with  the  artery  the  pres- 
sure of  the  blood  of  course  at  once  forces  the  mercury  down 
one  limb  of  the  tube  and  necessarily  up  in  the  other,  but  as 
the  recording  lever  moves  up  and  down  with  the  mercury 
on  which  it  rests  it  records  all  these  variations  in  pressure. 
An  examination  of  the  figure  of  the  kymograph  will  easily 
show  how  a  slight  increase  of  arterial  pressure  will  at  once 
cause  the  recording  lever  to  be  raised,  while  a  decrease  at 
once  lowers  it.  On  the  revolving  drum  this  recording  lever 
will  of  course  then  describe  curves  such  as  those  pictured 
in  Figure  86,  which  reproduce  in  excellent  detail  for  per- 
manent study  all  the  variations  of  pressure  in  the  artery  ex- 
amined. On  such  kymograph  tracings  as  those  traced  on 
the  drum  in  the  figure  here  given,  the  small  curves  indi- 
cate the  individual  pulse  waves,  or  what  is  the  same  thing 
finally,  the  heart  beats,  while  the  larger  waves  indicate  the 
movements  of  breathing.  In  the  case  of  a  dog  the  arterial 
pressure  rises  through  inspiration  and  sinks  during  expira- 
tion. The  explanation  of  this  periodic  respiratory  rise  and 
fall  of  arterial  pressure  is  not  yet  possible,  nor  has  it  been 
definitely  proved  that  it  exists  in  man.  If  we,  therefore, 
since  we  do  not  understand  fully  these  respiratory  curves, 
turn  our  attention  to  the  pulse  waves  themselves,  each  is 
seen  to  consist  of  a  straight  and  rapid  rise  of  pressure  to  a 
maximum  height,  while  the  fall  of  pressure,  or  the  down- 
ward wave,  is  not  at  all  straight  and  gradual.  There  is 


192 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


placed  on  the  descent  a  second  smaller  wave,  and  in  some 
instances  a  third.    The  second  wave,  however,  like  a  notch 


Fig.  86.— LUDWIG'S  KYMOGRAPH. 

A,  revolving  drum  to  receive  tracings;  JF?,  pendulum  of  the  clockwork  to  rotate  drum ; 
C,  the  U-shaped  mercury  tube ;  Z>,  where  connection  is  made  with  the  blood  vessel  to  be 
examined;  E,  F,  the  piston  raised  or  lowered  by  the  mercury  on  which  it  rests;  6,  the 
recording  lever. 


THE    CIRCULATION.  193 

on  the  descending  part  of  the  curve,  is  always  present. 
This  presence  of  two  crests  on  the  pulse  wave  has  given  to 
it  the  name  of  dichrotic.  The  explanation  of  this  second 
or  smaller  wave  superposed  on  the  first,  is  still  not  wholly 
satisfactory.  Various  suggestions  are  offered  by  different 
physiologists,  but  the  probability  is  that  the  second  wave  is 
due  to  the  reflection  of  the  pulse  wave  against  the  semi- 
lunar  valves. 

To  explain  this  more  fully  let  us  picture  the  condition 
of  things  just  at  the  moment  the  ventricle  forces  its  con- 
tents into  the  aorta.  Here,  in  order  to  make  room  for  the 
sudden  addition,  the  aorta  expands  close  to  the  heart, 
which  expansion  then  in  the  form  of  a  wave  proceeds  from 
that  point  to  the  periphery;  but,  like  the  waves  caused  by 
a  pebble  in  the  water,  they  would  naturally  run  in  all  di- 
rections, and  so  the  pulse  wave  would  start  to  run  back 
towards  the  heart.  But  scarcely  started  in  that  direction, 
it  would  meet  the  closed  semilunar  valves  and  be  there  re- 
flected backwards  on  the  heels  of  the  original  pulse  wave 
and  run  with  it  to  the  tips  of  the  arteries.  Just  as  a  loud 
sound  proceeding  in  a  certain  direction  might  have  upon 
its  heels  a  slight  echo  caused  by  some  precipice  just  behind. 

THE  INNEBVATION  OF  THE  BLOOD   VESSELS. 

Many  experiences  and  observations  show  that  blood  ves- 
sels have  a  nervous  control  separate  from  the  control  of  the 
heart.  Thus,  blushing  with  embarrassment,  or  turning 
pale  with  fright,  or  becoming  flushed  with  exercise  clearly  in- 
dicate that  nerves  must  affect  the  contraction  and  dilatation 
of  arteries.  The  fact  that  arteries  have  muscular  tissue  in 
their  walls  makes  such  a  contraction  or  dilatation  intelligible, 
and  no  doubt  the  nerves  in  question  reach  these  muscles. 
Experiments  have  not  failed  to  disclose  such  nerves  which, 
when  stimulated,  cause  the  arteries  either  to  contract  or 
expand.  Being  thus  concerned  in  controlling  the  motion 
of  the  muscles  of  the  arteries,  they  are  called  vaso-motor 
nerves.  In  their  physiological  effect  these  vaso-motor 


194  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

nerves  are  of  two  kinds;  first,  vaso-motor  nerves  which 
when  stimulated  cause  the  arteries  to  contract  —  the  vaso- 
constrictor nerves;  second,  vaso-motor  nerves  which  when 
stimulated  cause  the  arteries  to  dilate  —  vaso-dilator  nerves. 

1. — Vaso-consttictor  nerves.  The  vaso-constrictor  nerve 
fibres  are  found  in  almost  every  part  of  the  body.  They 
seem  in  a  continued  state  of  excitation,  keeping  the  arteries 
to  which  they  go  constantly  contracted,  for  when  such  a 
nerve  is  cut  the  arteries  affected  at  once  dilate.  The  ex- 
planation of  this  is  found  in  the  fact  that  the  cutting  of  the 
vaso-constrictor  nerves  puts  an  end  to  the  tonic  influence 
which  they  possess  and  the  arteries  freed  from  their  con- 
trol expand  to  their  natural  dimensions.  Why  the  arteries 
should  be  kept  continually  contracted  is  not  hard  to  under- 
stand. There  are  times  when  certain  organs  of  the  body 
in  order  to  do  special  work  need  an  extra  supply  of  blood. 
The  stomach  needs  more  blood  during  digestion  than  when 
idle  between  meals.  Now,  by  keeping  the  gastric  arteries 
in  a  tonic  or  continued  contraction  they  may  be  dilated  by 
relaxing  the  muscles  when  the  process  of  digestion  begins. 
As  arteries  cannot  forcibly  expand  (muscle  fibres  can  never 
be  made  to  expand  forcibly) ,  they  must  be  contracted  reg- 
ularly in  order  to  make  an  expansion  when  desired  pos- 
sible. While  cutting  a  constrictor  nerve  causes  a  dila- 
tation in  the  vessels  affected  because,  as  already  stated, 
the  tonic  control  is  cut  off,  a  stimulation  of  the  nerve 
causes  an  increased  contraction  in  the  artery  supplied.  If 
in  a  rabbit  the  constrictor  nerve  going  to  the  transparent 
ear  be  stimulated,  the  ear  flap  at  once  becomes  pale. 

Distribution  of  Faso- Constrictor  Nerves. 

The  course  of  these  constrictor  nerves  throughout  the 
body  is  about  as  follows:  First.  In  the  head  they  arise  in 
the  medulla,  pass  from  this  into  the  sympathetic  ganglia  of 
the  neck,  from  which  they  proceed  to  all  parts  of  the  head, 
usually  running  along  with  the  cranial  nerves.  The  tri- 
geminal  nerve,  especially,  is  rich  in  such  constrictor  fibres. 


THE   CIRCULATION.  195 

Second.  The  constrictor  nerves  of  the  chest  and  abdomen 
take  their  origin  in  the  medulla,  also,  then  through  the 
spinal  cord  they  reach  the  sympathetic  ganglia  of  the  chest 
and  abdomen  by  means  of  the  communicating  branches, 
and  from  these  ganglia  they  proceed  to  the  visceral  organs. 
The  constrictors  going  to  the  organs  in  the  abdominal 
region  go  mainly  through  the  large  splanchnic  nerves  and 
the  solar  plexus  from  which  they  spread  in  all  directions. 
As  there  are  so  many  and  such  large  arteries  in  the  ab- 
domen this  splanchnic  nerve  is  probably  the  most  important 
constrictor  nerve  in  the  body.  Third.  Constrictor  nerves 
going  to  the  trunk  and  the  extremities  arise  in  the  medulla, 
also,  pass  down  the  cord  and  through  the  communicating 
branches  reach  the  sympathetic  ganglia.  From  these  they  re- 
join the  spinal  nerves  and  with  them  are  distributed  at  the 
periphery.  It  will  thus  be  seen  that  all  the  constrictor  nerves 
arise  in  the  medulla,  but  that  before  reaching  their  destina- 
tion they  pass  through  sympathetic  ganglia.  For  this 
reason  they  are  often  called  sympathetic  nerves. 

The  Vaso- Constrictor  Center. 

These  nerves  are  governed  by  a  center  which  lies  in  the 
medulla  where  they  originate.  This  center  is  automatic, 
and  is  in  constant  excitation,  and  so,  as  stated  before,  there 
is  a  continued  contraction  in  all  the  arteries  supplied.  But 
this  vaso-constrictor  center  may  be  inhibited  in  part,  that 
is,  it  may  be  prevented  from  keeping  the  arteries  con- 
tracted. Such  an  inhibition  would,  of  course,  result  in  a 
dilatation  of  the  arteries  affected.  In  this  way  the  blood  sup- 
ply of  the  visceral  organs,  especially,  is  largely  controlled. 
What,  now,  are  the  influences  that  inhibit  this  center  and 
so  cause  a  dilatation? 

First:  Psychic  influences  inhibit  it.  The  explanation 
of  blushing  lies  in  the  fact  that  psychic  influences  (embar- 
rassment, shame,  etc.),  reach  that  part  of  the  center  con- 
trolling the  arteries  of  the  face  and  inhibit  it,  and  the 


196  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

muscles  freed  from  their  regular  control  relax  and  expand 
to  their  natural  dimensions. 

Second:  Different  afferent  nerves  may  inhibit  it.  When 
food  enters  the  stomach  the  sensory  impulses  reaching  the 
brain  from  the  stomach  inhibit  that  part  of  the  vaso-con- 
strictor  center  which  governs  the  gastric  arteries,  and  these 
removed  from  the  tonic  stimulus  to  remain  contracted  di- 
late, and  so  the  mucous  gastric  membrane  becomes  red  and 
flushed  with  blood. 

Third:  This  vaso-constrictor  center  is  very  energetic- 
ally inhibited  by  impulses  reaching  it  from  the  depressor 
nerves  of  the  heart.  As  stated  in  a  former  paragraph,  this 
tierve  is  probably  normally  stimulated  when  the  pressure  of 
the  blood  in  the  heart  (and  so,  of  course,  elsewhere),  be- 
comes too  great.  Such  impulses  on  reaching  the  vaso- 
constrictor center  in  the  medulla  forcibly  inhibit  it,  and  an 
immediate  dilatation  of  arteries  results,  the  consequence 
of  which  is  that  the  blood  pressure  at  once  sinks.  Such  a 
general  sinking  of  blood  pressure  is  usually  accomplished 
by  having  that  part  of  the  constrictor  center  inhibited  which 
governs  the  abdominal  viscera,  and  which  at  once  arrests 
the 'tonic  action  of  the  splanchnic  nerve.  As  a  result  of 
this  the  many  large  and  small  arteries  through  stomach 
and  intestines,  etc.,  enlarge,  the  blood  streams  through, 
and  the  arterial  pressure  is  relieved.  On  the  other  hand, 
to  stimulate  the  splanchnic  nerve,  that  is,  to  make  this  tonic 
action  stronger  and  so  produce  an  increased  contraction, 
may  diminish  the  size  of  the  abdominal  blood-vessels  to 
such  an  extent  as  to  press  out  of  them  as  much  as  twenty- 
seven  per  cent,  of  their  contained  blood  supply.  The  ef- 
ficiency of  and  the  necessity  for  such  a  nicely  regulated 
control  of  the  blood  supply  for  the  various  organs  is, 
of  course,  quite  apparent. 

Under  some  circumstances  this  constrictor  center  may 
be  actually  stimulated.  Thus,  turning  pale  with  fright  is 
due  to  the  flurried  stimulation  of  its  activity. 


THE    CIRCULATION.  197 

2. — Vaso-dilator  nerves.  In  addition  to  the  vaso-con- 
strictor  nerves  there  are  vaso-dilator  nerves.  These  nerves 
are  not,  however,  in  a  state  o-f  tonic  excitation,  but  are 
brought  into  play  at  special  times  only.  Thus,  when  a 
voluntary  muscle  is  made  to  exercise,  the  arteries  supplying 
that  muscle  at  once  dilate.  This  might  at  first  seem  due 
to  an  inhibition  of  that  part  of  the  constrictor  center  gov- 
erning the  arteries  of  these  muscles,  but  there  can  actually 
be  found  nerves  which  when  stimulated  cause  a  direct  di- 
latation. These  dilator  nerves  come  from  the  cerebro- 
spinal  system  and  are  most  apparent  in  the  voluntary  mus- 
cles and  numerous  glands  (submaxillary  wand  parotid) . 
They  run  to  the  intrinsic  ganglia  distributed  through  the 
muscular  coat  of  the  arteries  (to  which  also  the  vaso-con- 
strictor  nerves  run)  and  here  inhibit  the  action  of  these 
vaso-constrictor  nerves,  the  result  of  which  is,  of  course,  a 
dilatation.  They  run  along  with  the  trunks  of  the  cranial 
and  spinal  nerves,  and  anatomically  are  not  distinguishable 
from  them.  When  the  spinal  nerve  going  to  the  muscle  is 
cut  and  the  peripheral  end  stimulated  not  only  does  the 
muscle  contract,  but  the  artery  in  the  muscle  dilates.  Such 
dilator  nerves  serve  as  additional  means  to  regulate  the 
local  supply  of  blood,  and  in  the  case  of  muscles,  probably 
accompany  the  motor  nerves  so  that  the  best  activity  of  the 
muscle  would  be  made  possible  by  simultaneous  increase  in 
the  supply  of  blood  to  it.  The  vaso-dilator  center  lies  in 
the  medulla,  also,  but  seems  not  to  play  such  an  important 
role  as  the  constrictor  center. 

3. — Comparison  of  the  innervations  of  the  heart  and 
blood  vessels.  There  is  a  striking  homofogy  between  the 
nerves  of  the  heart  and  the  blood  vessels. 

1.  Both    have    distributed    in    their    muscles   intrinsic 
ganglia. 

2.  To  both  there  run  nerves,  the  stimulation  of  which 
causes  an  increase  in  the  contraction.     In  the  case  of  the 
heart  this  nerve  is  called  the  cardio-accelerator,  and  causes 


198  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  heart  to  contract  more  rapidly.  In  the  case  of  the  ves- 
sels it  is  the  vaso-constrictors.  These  nerves,  as  already 
stated,  when  stimulated  cause  an  increased  contraction  here. 
In  the  case  of  the  heart,  as  well  as  the  vessels,  these  nerves 
come  directly  from  the  sympathetic  system,  although  they 
take  their  real  origin  in  the  cerebro-spinal  system. 

3.  Both   heart   and   vessels   are   supplied   with   nerves 
which    inhibit;   that    is,    nerves,    a    stimulation    of    which 
causes  a  reduction  in  the  amount  of  contraction.     In  the 
case  of  the  heart  this  inhibitory  nerve  is  the  vagus,  pneu- 
mogastric,  or  tenth  cranial  nerve.     In  the  case  of  the  ves- 
sels it  is  the  vaso-dilators.     As  the  vagus  causes  the  heart 
muscle  to  relax,  so  the  dilators  cause  the  arterial  muscles 
to  relax.     In  both  cases  they  are  cerebro-spinal  nerves  and 
reach  their  destination  without  the  intervention  of  the  sym- 
pathetic system . 

4.  The  heart  is  supplied  with  an  accessory  nerve  called 
the  depressor,  which  carries  to  the  medulla  sensations  from 
the  cardiac  muscle.     While,  in  the  case  of  the  vessels  no 
such  a  typical  sensory  nerve  exists,  there   are,  of  course, 
distributed  to  them  nerves  of  general  sensation,  by  means 
of  which  sensory  impulses  from  them  reach  the  brain. 

CHANGES  IN  THE  CIRCULATION  WHICH  OCCUR  AT  BIRTH. 

It  is  evident  that  the  lungs  are  not  functional  before 
birth.  The  blood  must,  therefore,  seek  its  fresh  supply  of 
oxygen  elsewhere.  This  has  necessitated  the  blood  taking 
a  somewhat  different  course  up  to  the  moment  of  birth  from 
the  one  it  retains  ever  after. 

The  foetus  not  only  gets  its  nourishment,  but  its  oxygen 
supply  also  from  a  structure  known  as  the  placenta,  or 
"after-birth."  This  is  a  structure  which  grows  out  from 
the  foetus  and  intertwines  itself  closely  with  the  uterine 
wall;  so  closely,  indeed,  that  the  nourishment  in  the  blood 
flowing  through  the  uterus  may  seep  across  into  the  foetal 
capillaries  of  the  placenta,  and  along  with  it  the  oxygen 
carried  by  the  arterial  blood  of  the  mother  passes  through 


THE    CIRCULATION.  199 

the  capillary  walls  and  is  taken  up  by  the  foetal  red  cor- 
puscles. There  is,  of  course,  no  mixing  whatever  of  the 
maternal  and  foetal  bloods.  The  two  remain  perfectly  dis- 
tinct, and  the  transfer  of  nourishment  and  oxygen  is  made 
through  the  delicate  capillary  walls.  This  placenta  is, 
therefore,  the  foetal  lung.  Running  to  this  placenta  through 
the  umbilical  cord  or  naval  stalk  from  the  foetus  is  a  large 
artery  arising  from  the  abdominal  aorta.  This  carries  the 
blood  from  the  foetus  to  the  placenta.  Here  it  passes 
through  the  placental  capillaries  and  is  gathered  up  in  the 
veins  and  brought  back  to  the  foetus  through  the  umbilical 
cord  by  the  umbilical  vein.  This,  although  called  a  vein, 
contains  arterial  blood,  having  just  received  in  the  placenta 
both  its  new  supply  of  nourishment  and  oxygen.  Upon 
reaching  the  foetus  this  umbilical  vein  flows  through  the 
liver,  and  from  the  liver  the  blood  reaches  the  ascending 
vena  cava,  by  means  of  which  it  is  carried  to  the  right 
auricle.  This  pure  blood,  going  through  the  vena  cava 
in  the  way  just  described,  does  not  drop  from  the  right 
auricle  into  the  right  ventricle,  but  goes  from  the  right 
auricle  at  once  into  the  left  auricle  through  an  opening  in 
the  auricular  septum  called  the  foramen  ovale.  The  course 
of  blood  in  this  direction  is  facilitated  by  a  peculiar  flap  or 
valve  on  the  right  auricle  so  placed  that  it  guides  the  cur- 
rent of  blood  across  into  the  left  auricle.  This  little  flap  is 
called  the  Eustachian  valve.  This  transfer  is  materially 
aided  by  the  fact  that  the  ascending  vena  cava  flows  around 
to  the  back  of  the  right  auricle  before  emptying  into  it,  and 
so  has  its  opening  close  to  the  auricular  septum.  The  pure 
blood  so  transferred  to  the  left  auricle  now  drops  into  the 
left  ventricle,  and  by  its  systoles  is  forced  out  through  the 
aorta.  For  reasons  to  be  pointed  out  in  a  moment,  most  of 
this  pure  blood  goes  to  the  head  and  neck  through  the 
innominate  and  carotid  arteries.  Thus,  these  rather  more 
important  portions  of  the  body  are  supplied  with  the  best 
available  blood. 


200  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

•  From  these  regions,  that  is  from  head  and  neck,  the 
blood  is  again  gathered  up  by  veins,  and  finally  by  the  vena 
cava  descending,  carried  to  the  right  auricle.  But  here 
this  current  of  venous  blood  is  so  poured  into  the  right 
auricle  that  it  does  not  meet  the  current  of  pure  blood  flow- 
ing through  it  to  the  left  auricle.  The  descending  vena 
cava  opens  into  the  auricle  at  the  opposite  side  and  from 
above,  and  in  this  way  the  stream  of  venous  blood  which  it 
bears  at  once  drops  through  into  the  right  ventricle.  This 
crossing  of  two  streams,  one  arterial  and  one  venous  in  the 
right  auricle,  may  be  easily  understood  by  showing  how 
readily  one  might  construct  pipes  leading  into  a  room  in 
such  a  way  as  to  have  two  currents  flow  through  it  and  yet 
have  them  separate  and  distinct;  having  one,  for  instance, 
in  one  corner  drop  into  the  room  from  above,  into  a  collect- 
ing funnel  below,  while  the  other  stream  might  at  an  oppo- 
site corner  be  carried  across  from  one  wall  to  another  inde- 
pendently of  the  former,  especially  if  a  flap  or  plank  like 
the  Eustachian  valve  should  be  added. 

The  stream  of  venous  blood  having  reached  the  right 
ventricle  in  the  manner  described,  is  now  by  the  systole  of 
the  right  ventricle  forced  out  into  the  pulmonary  artery, 
and  would  naturally  go  to  the  lungs ;  but  the  lungs  do  not 
at  this  time  contain  air.  They  are  collapsed,  and  it  would 
be  almost  impossible  and  entirely  useless  to  force  this 
stream  of  blood  through  them.  This  difficulty  is  remedied, 
however,  by  a  communicating  branch  which  connects  the 
pulmonary  artery  with  the  arch  of  the  aorta,  and  so  enables 
the  venous  blood  to  pass  from  the  pulmonary  artery  through 
this  connecting  duct  into  the  descending  aorta.  This  con- 
necting duct  is  called  the  duct  of  Botallus.  As  this  duct 
of  Botallus  reaches  the  aorta  after  it  has  given  off  its  vessels 
to  the  head  it  prevents  the  flow  of  this  venous  stream  in 
that  direction.  But  this  venous  stream,  together  with  a 
little  pure  blood  which  finds  its  way  through  the  arch  of  the 
aorta  from  the  left  ventricle,  descends  ^ through  the  aorta, 
and  while  a  little  of  it  is  carried  by  arteries  which  supply 


THE   CIRCULATION.  201 

the  posterior  part  of  the  body,  most  of  it  is  again  by  the 
umbilical  artery  carried  to  the  placenta,  there  to  have  its 
oxygen  supply  renewed. 

At  the  moment  of  birth  a  number  of  changes  occur. 
The  circulation  of  blood  through  the  placenta  is  stopped, 
and  now  with  the  first  breath  drawn  into  the  lungs  these 
organs  expand  and  allow  the  stream  from  the  pulmonary 
arteries  to  pass  through  them.  Within  a  few  hours  the 
opening  from  one  auricle  into  the  other  begins  to  be  closed 
up,  and  the  duct  of  Botallus  becomes  filled  by  depositions 
of  fat  and  connective  tissue  in  its  lumen.  The  stumps  of 
the  umbilical  artery  and  vein  practically  disappear,  and  the 
circulation  which  is  to  be  maintained  throughout  life  is 
established.  It,  however,  not  infrequently  happens  that 
the  opening  in  the  auricular  septum  remains  through  life, 
and  in  some  cases  even  the  duct  of  Botallus  remains  open. 
Such  individuals,  must,  of  course,  have  their  circulation 
materially  interfered  with.  The  Eustachian  valve  in  the 
heart  becomes  almost  obliterated,  although  even  on  an 
adult  heart  traces  of  it,  as  well  as  the  thin  partition  closing 
the  auricular  septum,  and  the  solid  string,  the  remains  of 
the  duct  of  Botallus,  may  still  be  readily  seen.  In  this 
rather  remarkable  way,  without  a  break,  the  foetal  circula- 
tion becomes  changed  in  a  moment  into  the  regular  circu- 
lation of  the  fully  developed  body. 


CHAPTER  IX. 


THE  LUNGS  AND  THE  PROCESSES  OF 
RESPIRATION. 

The  circulation  of  the  blood  treated  in  the  preceding 
chapter  leads  naturally  and  without  a  break  to  the  consider- 
ation of  the  phenomena  of  respiration.  It  was  pointed  out 
that  the  main  reason  for  the  mad  rush  of  the  blood  is  to 
carry  out  the  functions  of  respiration.  Respiration  consists 
essentially  in  two  gaseous  interchanges.  One  of  these  takes 
place  in  the  lungs.  Here  oxygen  is  taken  up  by  the  red 
corpuscles  and  carbon  dioxide  thrown  off  from  the  plasma. 
The  second  gaseous  interchange  occurs  in  the  tissues  of  the 
body  and  is  the  exact  reverse  of  the  first,  for  here  the 
oxygen  is  liberated  and  the  carbon  dioxide  picked  up. 

These  two  respiratory  interchanges  are  complementary. 
The  one  in  the  lung  is  called  external  respiration,  the  one 
in  the  tissues  internal  respiration.  We  are  first  concerned 
with  the  processes  as  they  take  place  in  the  lungs. 

THE  ANATOMY  OF  THE  RESPIRATORY  SYSTEM. 

The  principal  structure  concerned  in  external  respir- 
ation is  the  lung.  Into  this  air  is  drawn  through  the  mouth 
and  nostrils  by  way  of  the  trachea.  At  the  upper  portion 
of  the  trachea  where  it  leads  into  the  pharynx  is  a  dilata- 
tion called  the  "  voice-box."  Here  by  suitable  arrange- 
ments the  outgoing  air  sets  into  vibration  stretched  mem- 
branes which  produce  the  sounds  of  speech.  For  a  detailed 
description  of  this  organ,  the  voice-box,  or  larynx,  the 
student  is  referred  to  a  subsequent  chapter  on  "The  Voice. ' ' 

The  windpipe,  or  trachea  as  it  is  called,  may  be  easily 
felt  by  placing  the  finger  on  the  throat.  The  large  dilated 
portion  is  the  voice-box  just  noted,  while  the  tube  extend- 
(202) 


THE    LUNGS    AND    RESPIRATION. 


203 


ing  downward  from  that  is  the  trachea  proper.  This  con- 
sists essentially  of  a  dense  fibrous  tissue  in  which  are  im- 
bedded horseshoe-shaped  pieces  of  cartilage  which  serve  to 


Fig.  87.— THK  AIR  PASSAGES  AND  LUNGS  FROM  BEFORE.     L,UNG  TISSUE  REMOVES  ON 

RIGHT   LUNG   TO   SHOW  RAMIFICATIONS   OF  BRONCHIAL   TUBES. 

a,  larynx;  b,  trachea;  d,  bronchial  tube. 

keep  the  trachea  open.  The  open  ends  of  these  horseshoes 
are  backward,  that  is,  next  to  the  gullet,  and  the  absence 
of  bands  of  cartilage  here  no  doubt  materially  facilitates 
swallowing. 

The  trachea  is  lined  on  the  inside  with  several  layers  of 
epithelial  cells,  of  which  the  innermost  layer  is  ciliated. 
These  cilia  move  in  regular  rhythm  and  in  such  a  way  that 
any  material  resting  on  them  is  driven  forward  toward  the 
mouth.  In  this  way  the  mucus,  or  phlegm,  is  removed. 
The  trachea  at  its  lower  end  divides  into  two  branches, 
called  the  bronchial  tubes,  and  these  in  turn  divide  and  sub- 
divide repeatedly  until  finally  a  perfect  system  of  ramifica- 
tions of  tubes  is  the  result.  At  the  end  of  each  of  these 
finer  ramifications  there  is  a  sack-like  dilation  called  the 
alveolus.  The  wall  of  this  alveolus  is  thrown  into  little 
pouches,  each  pouch  being  called  an  air  cell.  It  is  neces- 
sary to  remember  here  that  the  term  "cell"  is  not  used  in 


204 


STUDIES   IN   ADVANCED    PHYSIOLOGY. 


its  scientific  sense,  but  in  the  original  sense  it  had,  meaning 
a  little  chamber.     In  this  way  one  single  alveolus  may,  by 


Fig.  88.— CILIATED  EPITHELIUM  FROM  THE  TRACHEA  OF  A  RABBIT.     (After  Schafer.) 
w1,  m2,  m3,  mucus-secreting  cells  lying  between  the  ciliated  cells. 

the  folding  of  its  walls,  give  rise  to  a  great  many  air  cells. 
In  the  walls  of  these  air  cells  run  the  pulmonary  capillaries, 
and  at  this  point  the  gaseous  interchange  of  the  blood  takes 


Fig.  89. — DIAGRAMMATIC  REPRESENTATION  OF  THE  TERMINATION  OF  A  F.ROXCHIAL  TUBE 
.    IN  A  GROUP  OF  ALVEOLI.    (After  Schafer.) 

B,  bronchial  tube;    L.  £,  bronchiole;    A,  atrium;    1,  Alveolus;  c,  c,  individual   air 
cells. 

place.  The  anatomy  of  the  bronchial  tubes  and  their  finer 
divisions  does  not  differ  materially  from  that  of  the  trachea. 
The  cartilaginous  rings,  however,  become  less  regular  and 


THE    LUNGS    AND    RESPIRATION. 


205 


there  is  a  gradual  thinning  out  of  the  inner  epithelium, 
which  in  the  final  branches  is  reduced  to  a  single  layer 
of  ciliated  cells.  In  the  alveolus,  finally,  the  wall  is  made 
up  of  elastic  tissue  lined  on  the  inside  by  a  single  layer  of 
flat  epithelial  cells.  The  very  small  bronchial  tubes  pos- 
sess a  little  plain  muscular  tissue,  so  that  they  are  actually 
able  to  contract  and  expand,  and  thus  reduce  or  increase 
the  amount  of  air  which  reaches  the  alveolus.  The  space 
between  the  alveoli  and  the  branches  of  the  bronchial  tubes 
is  filled  with  connective  tissue,  through  which  nerves, 
arteries,  and  veins  pass. 


Fig.  90. — SECTION  OF  LUNG,  SHOWING  SEVERAL,  CONTIGUOUS  ALVEOLI,  WITH  THE  BLOOD- 
VESSELS IN  THE  SAME  INJECTED.     (After  F.  E.  Schultze.) 
a,  a,  c,  c,  partitions  and  edges  of  alveoli;  6,  artery  giving  off  capillaries. 

The  lung  is  covered  on  the  outside  by  a  delicate  serous 
membrane,  called  the  pleura.  This  surrounds  the  lung 
closely  at  all  points  except  at  the  root  of  the  lung,  the  point 
where  the  arteries  and  veins,  and  bronchial  tubes  enter  it, 
at  which  point  the  pleura  is  reflected  and  lines  the  inside  of 
the  chest  wall. 


206  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

PATHOLOGICAL  CONDITIONS  OF  THE  RESPIRATORY  SYSTEM. 

While  there  is  not  a  single  system  in  the  body  which  is 
immune  from  the  attacks  of  disease,  and  though  in  many 
individuals  the  respiratory  system  is  among  the  most  invul- 
nerable, yet  the  general  fact  remains  that  this  system  more 
than  any  other  becomes  the  seat  of  pathological  conditions. 
This  system  is  especially  apt  to  become  congested  and  in- 
flamed as  a  consequence  of  exposure  to  cold.  When  this 
inflammation  is  limited  to  the  trachea,  the  bronchial  tubes 
and  its  larger  divisions,  we  speak  of  it  as  a  mere  cold  on 
the  chest,  or  bronchitis.  As  a  consequence  of  a  congested 
condition  of  the  respiratory  mucous  membrane  it  frequently 
becomes  sore,  and  is  marked  by  an  excessive  secretion  of 
mucus,  often  to  such  an  extent  as  to  more  or  less  clog 
the  passages.  This  excessive  mucus  is,  of  course,  the 
familiar  phlegm,  which  forms  such  an  annoyance  of  an 
ordinary  cold.  Possibly  the  meaning  of  this  extra  mucous 
secretion  may  be  found  in  the  fact  that  it  acts  as  a  kind  of 
protection  to  the  inflamed  membrane  beneath,  and  serves 
to  prevent  the  introduction  into  that  membrane  of  foreign 
particles,  be  they  ordinary  grains  of  dust  or  more  injurious 
germs.  This  phlegm  is,  therefore,  figuratively  speaking, 
a  kind  of  natural  salve  which  nature  puts  over  these  con- 
gested portions  to  prevent  the  danger  of  exposure  to  foreign 
elements. 

This  congestion  may  also  extend  into  the  air  passages  of 
the  nose  and  so  produce  the  familiar  "  cold  in  the  head," 
and  as  the  mucous  membrane  of  the  pharynx  is  continued 
into  the  middle  ear  through  the  Eustachian  tube,  that  organ 
is  frequently  drawn  into  the  inflammation.  When  such  a 
congestion  of  the  nasal  passages  continues  and  becomes  the 
seat  of  ulcerations,  it  leads  to  the  too-common  catarrh. 
But  the  term  "  catarrh  "  is  not,  strictly  speaking,  confined 
in  its  application  to  a  chronic  inflammation  of  the  nasal  pas- 
sages. The  term  "catarrh"  means  inflammation,  and  in 
such  a  sense  is  applied  to  an  inflammation  wherever  it  may 
occur.  Thus,  bronchitis  is  but  a  catarrh  of  the  bronchial 


^HE   LUNGS   AND    RESPIRATION.  207 

tube-s.  An  inflammation  of  the  mucous  membrane  of  the 
stomach  is  called  a  "catarrh"  of  the  stomach,  while  even  an 
inflammation  of  the  eye  due  to  exposure  is  spoken  of  as  an 
ophthalmic  catarrh. 

As  long  as  the  inflammation  is  confined  to  the  larger  air 
passages  no  especial  danger  ensues.  But  this  inflammation 
may  become  extended  into  the  alveoli  of  the  lung.  This 
condition  is  a  much  more  serious  one,  and  is  called  pneu- 
monia. Colds,  catarrh  and  pneumonia  are  not,  however, 
mere  congestions.  If  they  were,  the  effects  of  the  conges- 
tion ought  to  disappear  when  the  proper  vascular  supply  is 
re-established.  These  diseases  owe  their  dire  results  to  the 
infection  of  germs.  The  bacterium  of  pneumonia  has  been 
recently,  actually,  quite  satisfactorily  isolated.  Arctic  ex- 
plorers report  their  perfect  immunity  from  colds  in  regions 
which  are  free  from  bacteria.  We  must  look  upon  the  con- 
gestion of  the  air  passages  or  lungs  more  as  a  favorable  cir- 
cumstance for  bacterial  infection,  which  infection  once  hav- 
ing secured  a  foothold,  produces  the  real  disease.  That  the 
resistance  of  the  respiratory  organs  to  germs  is  materially 
weakened  in  congestions  is  attested  by  the  relative  ease 
with  which  consumption  is  induced  in  weak  persons,  as  a 
consequence  of  a  "  cold." 

The  pleura,  also,  may. become  the  seat  of  inflammation, 
giving  rise  to  a  disease  called  pleurisy. 

The  smaller  bronchial  tubes  near  to  where  they  open 
into  the  alveoli,  possess  in  their  walls  some  plain  muscular 
fibres.  Ordinarily  these  are  relaxed  and  so  free  access  of 
air  is  permitted  to  the  alveoli.  But  under  certain  conditions 
these  muscles  go  into  a  tonic  contracted  state,  thus  materi- 
ally reducing  the  quantity  of  air  which  is  able  to  get  into 
the  alveolus  and  so  making  it  difficult  for  the  person  in 
question  to  get  a  sufficient  amount  of  air.  This  condition 
is  called  asthma. 

Finally,  the  most  serious  pathological  condition  of  the 
lung  is  consumption.  This,  as  has  been  pointed  out,  is  a 
disease  which  is  due  to  the  ravages  of  bacteria  living  in  that 


208  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

organ.  When  we  remember  that  on  an  average  about  every 
one  person  in  seven  is  afflicted  with  this  disease,  that  it  car- 
ries off  as  its  prey  more  people  than  pretty  nearly  all  of  the 
more  violent  contagious  diseases  combined,  and  when  we 
remember  that  by  improper  ventilation,  the  crowding  of 
persons  into  close  rooms,  this  disease  is  highly  communica- 
ble, we  are  more  than  justified  in  every  reasonable  effort  to 
prevent  its  spread,  and  especially  its  spread  to  children, 
who,  on  account  of  their  age,  may  yet  happily  be  free  from 
its  fatal  touch. 

•* 

THE  MECHANICS  OF  RESPIRATION. 

1. — Movements  of  Respiration.  In  order  for  the  blood 
to  be  continually  supplied  with  fresh  oxygen  it  is  necessary 
that  this  gas  should  be  constantly  renewed  in  the  lungs. 
This  renewal  is  brought  about  by  the  movements  of  respira- 
tion. The  essential  feature  of  all  the  movements  of  in- 
spiration is  an  enlargement  of  the  chest.  By  enlarging  the 
chest  additional  room  is  made,  and  the  air  rushes  in  from 
the  outside  to  occupy  this  extra  space.  Just  as  in  an  ac- 
cordion when  it  is  drawn  apart,  air  streams  into  it  through 
the  various  valves  made  for  that  purpose.  Or,  as  in  the 
case  of  a  pump,  when  the  piston  is  lifted,  and  so  additional 
room  made  in  the  pump  cylinder,  the  water  under  the  pres- 
sure of  the  atmosphere  rushes  in  to  fill  this  extra  space. 
This  enlargement  of  the  chest  may  occur  in  three  different 
ways. 

First,  it  may  be  enlarged  in  an  up-and-down  direction. 
This  is  accomplished  by  the  contraction  of  the  muscles  of 
the  diaphragm.  The  diaphragm  is  a  dome-shaped  structure 
with  the  dome  or  convexity  extending  chestward.  By  the 
contraction  of  the  muscles  in  this  dome  it  is  pulled  down- 
ward, the  dome  becomes  flattened  and  the  chest  cavity  en- 
larged a  corresponding  amount. 

Second,  fhe  chest  may  be  enlarged  by  increasing  its 
dimensions  in  a  forward-back  direction.  This  is  done  by 
raising  the  breast  bone.  By  noting  the  skeleton  it  may  be 


THK    LUNGS   AND    RESPIRATION.  209 

seen  that  the  breast  bone  is  connected  with  numerous  pairs 
of  ribs  which  extend  from  the  breast  bone  backwards  and  up- 
wards. If,  now,  by  proper  muscles  these  ribs  are  raised, 
the  result  will  be  that  not  only  the  breast  bone  will  move 
upward,  but  also  forward.  This  may  readily  be  exemplified 
by  joining  both  hands  and  letting  them  rest  in  front  on  the 
pelvic  region.  If,  now,  the  arms  be  raised  up,  not  only  are  the 
hands  raised,  but  they  are  also  pushed  away  from  the  body, 
and  when  the  arms  are  extended  directly  forward  may  be 
almost  two  feet  or  more  from  the  trunk,  whereas  in  their 
original  position  they  rested  immediately  against  it. 

A  third  enlargement  of  the  chest  is  the  lateral  enlarge- 
ment. This  is  brought  about  by  the  fact  that  not  only  are 
the  ribs  lifted  up,  but  they  rotate  outward.  This  enlarge- 
ment may  be  illustrated  in  the  example  of  the  raising  of  the 
folded  hands  also.  If,  in  addition  to  the  lifting  of  the 
hands,  as  in  the  preceding  illustration,  the  arms  be  some- 
what bent  and  rotated  outwards,  it  is  at  once  apparent  that 
the  lateral  diameter  is  increased. 

While  an  inspiration  results  from  an  enlargement  of  the 
chest,  an  expiration  is  due  to  a  contraction  of  the  chest. 
Under  ordinary  circumstances  an  expiration  is  a  passive 
process.  We  expand  the  chest  and  take  air  in  by  an  active 
contraction  of  muscles,  but  we  expire  by  simply  relaxing 
the  muscles  and  letting  the  chest  drop  back  to  its  natural 
dimensions.  Sometimes,  however,  the  expiration  may  be- 
come forced.  This  may  be  accomplished  in  three  different 
ways,  which  are  the  exact  opposites  of  those  given  for  en- 
larging the  chest.  That  is,  the  diaphragm  may  be  pushed 
up  further  into  the  chest  and  become  more  dome-shaped 
than  before.  This  is  done  by  contracting  the  abdominal 
muscles  and  so  pressing  the  stomach,  liver  and  intestines 
up  against  the  diaphragm,  and  in  this  way  lifting  it  up. 
Or,  a  forced  expiration  may  result  from  pulling  the  breast 
bone  downwards  and  rotating  the  ribs  inward. 

It  is  unnecessary  to  say  that  generally  all  three  ways  are 
used  at  the  same  time,  although  the  breathing  of   men  is 
14 


210  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

more  largely  with  the  diaphragm,  while  that  in  women  is 
more  largely  with  the  ribs. 

The  muscles  that  move  the  ribs  up  and  down  are  called 
the  intercostal  muscles.  Of  these  muscles  there  are  two 
sets,  the  external  intercostals  and  the  internal  intercostals. 
The  external  intercostals  are  so  arranged  that  the  insertion 
point  on  the  lower  rib  is  always  forward  from  the  insertion 
on  the  upper  rib,  while  in  the  internal  intercostals  the  re- 
verse is  true.  To  show  how  the  contraction  of  the  ex- 
ternal intercostals  raise  the  ribs  and  breast  bone,  while  the 


Fig.  91. — DIAGRAM  TO  ILLUSTRATE  THE  MANNER  OF  ENLARGEMENT  OF  CHEST. 

internal  intercostals  pull  it  down,  a  little  piece  of  apparatus 
may  be  constructed  such  as  the  one  indicated  in  the  accom- 
panying diagram.  If,  now,  a  piece  of  rubber  be  stretched 
in  such  a  way  as  to  correspond  with  the  pull  of  the  ex- 
ternal intercostals  it  will  raise  the  bars.  When  arranged 
like  the  internal  intercostals  it  will  pull  it  forcibly  down- 
wards. That  such  would  result  is  of  course  easily  seen  by 
studying  Figure  92.  The  line  a  b' ,  corresponding  to  the  ex- 
ternal intercostals  is  shortened,  which,  of -course,  is  analo- 
gous to  the  contraction  of  the  muscle  itself.  Shortening  can 
take  place  only  when  both  beams  are  pulled  upward,  while 
the  exactly  opposite  is  the  result  with  the  internal  inter- 
costals. 

2. — The  Rate  of  These  Movements.  The  rate  at  which 
inspirations  follow  each  other  varies  considerably  under 
different  circumstances,  but  on  an  average  in  an  individual 


THE    LUNGS    AND    RESPIRATION. 


211 


who  is  not  conscious  that  his  breathing  movements  are 
being  observed,  the  rate  is  from  fifteen  to  twenty  per 
minute.  It  is  greater  in  children,  and  in  infants  is  on  an 


Fig.  92.— DIAGRAM  TO  SHOW  THE  OPERATION  OF  THE  EXTERNAL  AND  INTERNAL  INTER- 
COSTAL MUSCLES. 
R,  R",  r,  r",  ribs  in  elevated  position;  R,  R',  r,  r',  ribs  in  depressed  condition;  a,  6. 

external  intercostals;  a',  &',  same  contracted  elevating  the  ribs;  d',  c',  internal  intercos- 

tals;  d,  c,  same  contracted  depressing  ribs. 

average  as  high  as  forty-four.  From  this  it  gradually  sinks 
during  childhood  until  the  adult  rate  of  fifteen  to  twenty 
just  given  is  reached.  This  rate,  however,  may  be  much 
influenced  by  emotions,  by  muscular  exercise  and  by  tem- 
perature. 

3. — The  Capacity  of  the  Lungs.  The  capacity  of  the 
lungs  no  less  than  the  rate  varies  with  different  classes  of 
people,  and  even  with  individuals  of  the  same  class.  On 
an  average,  however,  in  a  properly  exercised  person  the 
following  figures  do  not  come  very  far  from  the  actual  con- 
dition of  things : 

If  a  person  breathe  out  as  much  air  as  he  can  possibly 
do,  or,  in  other  words,  if  he  reduce  the  capacity  of  his 
lungs  as  far  as  he  is  able  to  do,  he  still  has  in  his  lungs  a 
considerable  amount  of  air.  During  life  it  is  impossible,  of 
course,  to  get  the  lung-  perfectly  air  free,  and  so  the  amount 
of  air  which  is  left  in  the  lung  after  the  most  forced  ex- 
piration possible,  can  be  measured  only  after  death.  Ex- 
periments of  this  kind  give  about  1,640  centimeters,  or 


£12  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

about  100  cubic  inches  as  the  amount  of  air  which  it  is  im- 
possible, even  by  the  most  violent  expiration,  to  remove. 
These  100  cubic  inches  are  called  the  " residual'7  air.  But 
in  ordinary  respirations  we  do  not  breathe  out  as  much  as 
we  can,  and  under  these  circumstances  there  is  left  in  the 
lung  1,640  centimeters,  or  100  cubic  inches  additional. 
That  is  to  say,  in  ordinary  breathing  there  are  in  the  lung 
at  the  end  of  an  expiration  200  cubic  inches  of  air.  These 
extra  100  cubic  inches  are  called  the  "supplemental"  air, 
which,  together  with  the  residual  air,  forms  the  *  'stationary" 
air  of  200  cubic  inches.  Now,  at  an  ordinary  breath  we 
take  in  about  500  centimeters,  or  30  cubic  inches,  and  of 
course  breathe  out  the  same  amount  at  an  ordinary  breath. 
This  air  is  called  the  "tidal"  air.  But  we  are  able  by  a 
forced  inspiration  to  take  in  more  than  we  do  ordinarily. 
We  seldom  breathe  as  deeply  as  we  can.  By  a  forced  in- 
spiration the  lung  is  able  to  take  in  100  cubic  inches  more. 
These  extra  100  cubic  inches  are  called  the  "complemental" 
air.  The  amount  of  air  which  one  is  able  to  breathe  from 
the  deepest  expiration  possible  to  the  deepest  inspiration 
possible  is  called  the  "vital  capacity."  This  would  then 
consist  of  the  supplemental  air,  100  cubic  inches,  the  tidal 
air,  30  cubic  inches,  and  the  complemental  air,  100  cubic 
inches.  In  all  230  cubic  inches;  that  is,  approximately  an 
even  gallon. 

Such  determinations  of  the  capacity  of  the  lung,  of 
course  with  the  exception  of  the  residual  air,  may  be  easily 
made  by  means  of  the  spirometer,  an  instrument  found  in 
almost  every  well-equipped  gymnasium. 

4. — The  Amount  of  Air  Used.  In  the  mechanics  of  res- 
piration there  have  been  considered  so  far  the  following 
topics:  1.  The  movements  of  respiration,  or  those  changes 
by  means  of  which  the  capacity  of  the  chest  is  enlarged  and 
contracted,  and  so  the  air  drawn  into  it  or  forced  out.  2. 
The  rate  of  these  movements.  3.  The  capacity  of  the 
average  lung.  A  very  important  topic  in  the  mechanics  of 
breathing  still  remains  to  be  answered.  It  is  the  question 


THE    IvUNGS    AND    RESPIRATION.  213 

of  the  amount  of  air  necessary  to  properly  supply  the  lungs, 
which  includes  the  rather  important  subject  of  ventilation. 

Ventilation. 

As  stated  before,  we  take  in  at  each  breath  about  thirty 
cubic  inches  of  air;  that  is,  about  half  a  liter.  As  about 
fifteen  breaths  are  taken  on  an  average  per  minute,  this 
makes  the  amount  of  air  taken  into  the  lungs  in  that  time 
450  cubic  inches.  But  the  problem  of  the  amount  of  air  is 
not  so  simple  as  that.  If  each  mouthful  of  air  as  it  is 
breathed  out  could  at  once  be  snatched  away  from  the  mouth 
and  so  enable  a  fresh  mouthful  to  be- taken  in,  450  cubic 
inches  would  suffice.  By  making  careful  experiments  it  has 
been  shown  that  every  mouthful  of  air  that  we  breathe 
out  is  mixed  with  the  outside  air  and  vitiates  three  times  as 
much  additional  air,  to  such  an  extent  as  to  make  it  no 
longer  fit  for  respiration.  Or,  in  other  words,  every  mouth- 
ful we  breathe  becomes  mixed  with  three  additional  mouth- 
fuls  outside,  in  a  way  to  make  the  four  mouthfuls  so  result- 
ing perfectly  unfit  for  further  respiration.  Therefore,  the 
amount  of  air  actually  required  per  minute  is  not  450  cubic 
inches,  but  four  times  450  cubic  inches,  or  1,800  cubic 
inches  per  minute.  This  is  just  a  little  over  one  cubic  foot. 
These  figures  express  rather  important  results  and  ought  to 
be  kept  in  mind  by  persons  who  have  the  ventilation  of 
crowded  rooms  in  charge.  Fresh  air  ought  to  be  admitted 
at  the  rate  of  one  cubic  foot  per  minute  for  each  person  in 
the  house.  This  does  not,  of  course,  mean  the  production 
of  a  draft,  it  being  entirely  possible  to  renew  the  air  at  this 
rate  even  in  a  fairly  crowded  room  without  subjecting  any 
body  in  it  to  exposure  to  a  draft. 

For  proper  ventilation  an  amount  of  space  between 
500  and  1,000  cubic  feet  for  each  person  ought  to  be  avail- 
able. In  some  of  the  better  hospitals  where  the  crowding 
of  patients  is  not  permitted,  "and  where  the  subject  of  proper 
ventilation  is  treated  as  of  the  primest  importance,  the 
amount  of  space  allowed  to  each  patient  is  often  even  more 


214  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

than  this.  These  figures  ought  not  to  be  passed  over 
thoughtlessly,  but  ought  to  serve  as  a  criterion  in  judging 
whether  any  room  in  question  is  really  capable  of  housing 
one,  or  two,  or  three  individuals,  as  the  case  may  be. 
Students,  especially,  are  sometimes  not  overly  careful  in. 
crowding  two  or  three  into  a  small  room,  the  capacity  of 
'I  which  would  be  but  little  more  than  that  required  for  a 
single  occupant. 

Wliat  Vitiates  Air? 

It  was  pointed  out  that  in  breathing,  oxygen  is  taken 
from  the  air  and  carbon  dioxide  given  to  it.  But  air  be- 
comes vitiated  and  is  no  longer  fit  to  be  breathed,  not  be- 
cause too  much  of  the  oxygen  has  been  removed,  or  because 
too  much  carbon  dioxide  is  present  in  it.  In  an  atmosphere 
in  which  the  amount  of  oxygen  should  be  materially  reduced 
the  blood  could  still  get  all  of  that  gas  it  would  need.  An 
atmosphere  containing  quantities  of  carbon  dioxide  very 
much  greater  in  proportion  than  that  in  the  air  of  badly 
ventilated  rooms,  would  still  be  perfectly  harmless  to 
breathe.  Of  course  if  the  oxygen  supply  should  be  reduced 
so  much  as  to  make  it  impossible  to  get  enough  of  that  gas, 
or  if  there  should  be  so  much  carbon  dioxide  in  the  atmos- 
phere that  it  would  almost  entirely  replace  the  oxygen,  as 
it  is  sometimes  in  deep  wells  or  in  mines,  then  the  carbon 
dioxide  would  prove  injurious  and  fatal,  but  not  because  it 
itself  is  injurious  or  poisonous,  but  simply  because  it  has 
displaced  the  necessary  oxygen. 

The  thing  that  makes  air  which  has  been  breathed  once 
no  longer  fit  for  respiration  is  the  fact  that  such  expired  air 
contains  organic  impurities  which  have  been  breathed  out 
from  the  lungs.  It  is  impossible  to  determine  just  what  these 
impurities  are,  but  they  are  probably  volatile  substances  of  a 
poisonous  nature,  or  may  actually  be  particles  of  decayed 
lung  or  other  organic  tissue.  It  is  this  organic  admixture 
that  plays  havoc  in  instances  of  insufficient  ventilation.  An 
idea  of  the  large  amount  of  such  organic  material  breathed 
out  may  be  gained  when  we  remember  how  frequently  the 


THE    LUNGS    AND    RESPIRATION.  215 

breath  of  persons  is  tainted  more  or*  less  strongly  with  ob- 
jectionable odors,  which  in  many  cases  are  not  necessarily 
due  to  a  careless  condition  of  the  teeth,  but  due  to  sub- 
stances either  volatile,  or  to  small  particles  of  disintegrated 
tissue  which  have  emanated  from  the  lungs.  Our  bodies 
seem  peculiarly  susceptible  to  such  eliminated  particles,  and 
an  atmosphere  that  has  been  vitiated  even  to  a  small  extent 
with  them  becomes  at  once  unpleasant  to  our  nostrils,  and 
if  in  spite  of  this  warning  we  persist  in  breathing  it,  there 
results  finally  a  dullness,  a  headache,  or  a  general  indisposi- 
tion which,  if  continued  from  day  to  day,  surely  and  inevit- 
ably leads  to  an  undermining  of  the  general  health  and 
energies,  and  may  succeed  in  cutting  the  life  unnaturally 
short. 

There  are  persons  who  seem  to  think  that  the  import- 
ance of  ventilation  as  it  is  urged*  by  persons  who  have 
studied  that  subject  is  somewhat  of  a  scientific  fad,  and  the 
day  is  not  yet  here  when  persons  who  have  the  ventilation 
of  crowded  rooms  in  charge  always  appreciate  the  impor- 
tance of  the  duty  so  assigned  to  them.  In  determining  the 
amount  of  air  which  ought  to  be  admitted  into  a  room, 
stoves  which  consume  large  quantities  of  oxygen,  or  gas  jets 
which  use  up  a  certain  supply  of  the  same  gas,  must  be 
taken  into  consideration,  for  the  consumption  of  oxygen  in 
a  stove  may,  under  certain  circumstances,  be  many  times 
that  of  a  single  person.  Then,  further,  as  there  are  always 
emanating  from  a  heated  stove  certain  poisonous  gases,  the 
necessity  for  a  more  perfect  ventilation  than  ordinary  is  at 
once  apparent > 

THE  CHEMISTRY  OF  RESPIRATION. 

1. — Composition  of  Inspired  and  Expired  Air.  The 
composition  of  the  air  which  we  inspire  is  about  as  follows : 

Nitrogen 79  per  cent. 

Oxygen 20        " 

Carbon  Dioxide 004        " 

Water  in  amounts  depending  on  the  humidity  of  the  atmosphere. 


216  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

In  addition  to  these  gases  there  was  recently  discovered 
another  gas  resembling  nitrogen  in  some  of  its  properties, 
and  called  "Argon"  by  its  discoverer,  but  as  this  gas  does 
not  figure  in  the  processes  of  respiration  a  consideration  of 
it  may  be  for  our  purposes  omitted. 

If  now  with  such  inspired  air  we  compare  expired  air, 
we  find  that  a  number  of  changes  have  occurred  in  the 
lungs.  First,  the  expired  air  is  warmer,  due  to  its  having 
remained  for  some  time  in  the  warm  lung.  Second,  as  a 
consequence  of  this  increase  in  temperature  it  has  expanded 
slightly  in  volume,  so  that  the  expired  air  seems  at  first  a 
little  larger  than  inspired  air,  and  for  this  reason  it  tends 
to  rise.  However,  when  expired  air  is  reduced  to  the  same 
temperature  and  pressure  as  the  inspired  air,  it  is  found  to 
be  a  little  less  in  volume,  showing  that  a  part  of  the  air  has 
actually  been  taken  into  the  body  and  kept  there.  Third,  ex- 
pired air  contains  a  much  larger  amount  of  moisture.  This 
is  especially  evident  on  a  cold  day  when  the  breath,  as  we 
say,  becomes  visible,  due  to  the  condensation  of  the  large 
amount  of  moisture  in  it.  So  far  the  changes  are  merely 
physical  changes.  There  is,  however,  fourth,  quite  a  dif- 
ference in  the  chemical  composition  of  the  two.  The  ex- 
pired air  has  lost  five  per  cent,  of  oxygen  and  gained  about 
four  per  cent,  of  carbon  dioxide,  and  finally,  fifth,  the 
expired  air  contains  traces  of  volatile  organic  substances, 
and  possibly  particles  of  disintegrated  tissue  to  which  the 
vitiation  of  respired  air  is  due. 

It  requires  special  chemical  experiments  to  show  that 
five  parts  of  the  twenty  parts  of  oxygen  have  been  removed. 
On  the  other  hand,  the  addition  of  the  four  parts  of  carbon 
dioxide  to  expired  air  may  be  easily  shown  in  a  very  simple 
experiment.  If  a  person  breathe,  by  means  of  a  glass  tube, 
"through  a  flask  or  bottle  containing  lime-water,  the  carbon 
dioxide  will  unite  with  the  lime-water,  and  a  white  precipi- 
tate will  form  insoluble  in  the  water  which  soon  settles  to 
the  bottom. 


THE    LUNGS    AND    RESPIRATION.  217 

The  composition  of  expired  air  may  then  be  tabulated 
as  follows: 

Nitrogen 79  per  cent. 

Oxygen 15        " 

Carbon  Dioxide 4        "' 

Water  in  increased  amounts. 
Organic  substances. 

2. — The  Amount  of  Oxygen  Consumed  in  One  Day  and 
the  Amount  of  Carbon  Dioxide  Eliminated  in  the  same 
Period.  As  the  amount  of  oxygen  which  is  taken  up  by 
the  blood  while  in  the  lung  is  five  per  cent,  of  the  entire 
air,  we  are  easily  able  to  calculate,  knowing  the  amount  we 
breathe  in  at  each  breath  and  the  number  of  breaths  in  a 
given  time,  just  how  much  oxygen  under  ordinary  pressure 
we  can  consume  in,  say  a  day.  Such  calculations  give  as 
the  daily  oxygen  consumption  twenty  to  twenty-five  cubic 
feet.  The  carbon  dioxide  is  a  little  over  four  per  cent,  and 
in  a  day  amounts  to  from  sixteen  to  eighteen  cubic  feet. 

To  all  students  who  have  taken  even  elementary  courses 
in  chemistry,  oxygen  and  carbon  dioxide  are  things  of 
knowledge.  For  the  sake  of  persons  who  have  had  no 
training  in  chemistry  it  may  be  in  place  here  to  refer  briefly 
to  the  nature  of  these  two  substances. 

Oxygen  is  a  gas  which  forms  about  a  fifth  of  the  ordi- 
nary atmosphere,  and  is  that  element  of  the  atmosphere 
which  makes  burning  possible.  It  is  ordorless,  tasteless, 
colorless,  and  so  not  easily  perceived  by  the  senses,  yet 
forming  an  integral  part  of  the  very  atmosphere  in  which  we 
move,  and  chemically  familiar  to  everybody  as  the  element 
in  the  atmosphere  which  as  the  draft  we  lead  into  stoves  and 
lamps  to  make  combustion  possible,  it  needs  no  further  ex- 
planation. Pure  oxygen  very  materially  increases  the  energy 
of  combustion,  and  in  an  atmosphere  of  pure  oxygen  even 
such  an  apparently  incombustible  thing  as  a  steel  wire  may 
be  made  to  burn  easily.  In  the  air,  however,  the  oxygen  is 
very  much  diluted  with  the  inert  gas  called  nitrogen  which 
serves,  therefore,  in  this  process  of  respiration  as  a  mere 
diluting  agent  and  plays  no  active  role  itself. 


218  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

Carbon  dioxide  (COL.)  is  the  gas  which  results  when 
carbon,  or  things  which  contain  carbon,  such  as  \vood  or 
coal,  are  burned.  It  is  colorless,  and  in  diluted  amounts 
tasteless  and  odorless,  and  so  not  readily  perceived  when 
mixed  with  the  gases  of  the  atmosphere.  In  a  pure  form 
carbon  dioxide  is  familiar  as  the  gas  which  rises  from  a 
freshly-drawn  glass  of  soda-water,  the  soda  fountains  being 
charged  and  the  pressure  in  them  produced  by  this  gas. 
It  is  the  gas  which  causes  the  effervescence  when  vessels 
containing  any  of  the  so-called  ((  sparkling  liquids, "  such 
as  pop  or  champagne,  are  opened. 

THE  PHENOMENA  OF  EXTERNAL  RESPIRATION. 

1. — The  Supply  of  Oxygen.  Possibly  the  best  way  to 
arrive  at  a  proper  understanding  of  the  exact  way  in  which 
the  gaseous  interchange  in  the  lungs  is  accomplished  is  to 
get  a  clear  picture  of  the  actual  condition  of  things  in  that 
organ.  In  the  first  place,  in  the  alveoli  is  fresh  air,  brought 
there  by  the  movements  of  respiration.  In  the  walls  of 
these  alveoli  lie  the  pulmonary  capillaries,  into  which  the 
venous  blood  coming  from  the  right  side  of  the  heart  enters. 
This  venous  blood  in  the  capillaries  is  separated  from  the 
air  in  the  alveoli  by  the  membranes  which  form  the  walls 
of  the  capillaries  and  the  linings  of  the  alveoli.  Thus  there 
seems  to  be  at  first  a  difficulty  in  having  the  air  and  the 
blood  put  in  direct  contact.  Experiments,  however,  show 
that  a  moist  membrane  which  may  separate  a  liquid  from  a 
gas  may  be  for  all  practical  purposes  disregarded.  Thus, 
if  a  glass  vessel  be  taken,  filled  with  a  certain  liquid  and  a 
moist  membrane  stretched  carefully  over  it,  and  then  the 
vessel  be  put  into  an  atmosphere  of  a  certain  gas,  the  result 
will  be  much  the  same  as  if  that  membrane  had  been  left 
entirely  off,  the  only  difference  being  that  the  presence  of 
the  membrane  slightly  retards  the  rapidity  of  the  gaseous 
interchange.  Thus  this  apparent  difficulty  at  once  disap- 
pears and  we  may  therefore  imagine  the  venous  blood  of  the 
capillaries  and  the  air  in  the  alveoli  in  immediate  contact. 


THE    LUNGS    AND    RESPIRATION.  219 

The  next  question  that  suggests  itself  is  the  exact  man- 
ner in  which  the  gases  of  the  air  enter  the  blood,  and  how 
those  of  the  blood  enter  the  air.  In  order  to  understand 
this  it  is  desirable  to  turn  aside  a  little  and  explain  some- 
what in  detail  one  of  the  most  familiar  laws  of  the  physical 
laboratory,  the  law  which  governs  the  absorption  of  gases 
by  liquids. 

D ALTON'S  LAW  OF  THE  ABSORPTION  OF  GASES  BY  LIQUIDS. 

When  in  any  experiment  a  liquid  and  a  gas  are  brought 
together  the  liquid  will  at  once  absorb  or  dissolve  in  itself 
some  of  this  gas,  the  amount  so  dissolved  depending  on  the 
pressure  which  that  gas  exerts  on  the  liquid,  and  varying  di- 
rectly with  that  pressure.  This  is  not  a  physiological  phe- 
nomenon but  a  general  physical  law,  and  applies  to  all  liquids 
and  gases.  It  was  named  after  the  physicist  who  first  care- 
fully proved  and  formulated  the  law,  and  called  "  Dalton's 
L,aw  of  the  Absorption  of  Gases."  This  law  of  the  absorp- 
tion of  gases  announces  the  observed  fact  that  the  amount 
of  gas  which  any  liquid  absorbs  depends  on  the  pressure 
which  that  gas  exerts  on  the  liquid  and  varies  directly  with 
it;  that  is,  if  the  pressure  is  doubled  the  amount  of  gas  so 
dissolved  is  doubled ;  if  the  pressure  is  reduced  to  one-half 
the  amount  of  gas  dissolved  is  reduced  one-half. 

There  are  many  familiar  illustrations  of  this  law.  For 
instance,  in  the  manufacture  of  the  familiar  soda-water  it  is 
deemed  desirable  to  have  ordinary  water  absorb  very  large 
quantities  of  carbon  dioxide.  Under  ordinary  pressure 
water  absorbs  but  little  carbon  dioxide,  but  to  remedy  this, 
the  water  to  be  made  into  soda-water  is  subjected  in  a 
proper  system  of  tanks  to  a  very  great  pressure  of  the  car- 
bon dioxide  gas,  and  in  conformity  to  Dalton's  law  the  water 
absorbs  increased  quantities  of  that  gas.  The  heavier  the 
pressure  in  such  a  charged  soda-fountain,  the  more  gas  will 
the  water  absorb.  The  same  thing  is  illustrated  in  the  bot- 
tling of  mineral  waters.  Here  the  ordinary  water  is  sub- 
jected to  a  high  pressure  of  carbon  dioxide  gas,  too,  and 
under  this  high  pressure  the  mineral  water  dissolves  into  it- 


220  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

• 

self  increased  quantities,  and  in  that  condition  is  forced  into 
bottles  which  are  then  tightly  sealed,  in  order  to  retain  the 
gas  at  the  original  pressure.  A  bottle  of  mineral  water  that 
had  been  filled  from  a  tank  subjected  to  a  carbon  dioxide 
pressure  twice  as  great  as  that  of  a  second  tank  would  have 
twice  as  much  carbon  dioxide  gas  in  it  as  a  similar  bottle 
filled  from  the  second  tank. 

The  water  of  our  wells  and  streams  is,  of  course,  in 
contact  with  the  air,  and  the  air  presses  on  it  with  a  pres- 
sure equal  to  fifteen  pounds  to  the  square  inch.  In  conform- 
ity to  the  law  just  given  certain  and  definite  amounts  of  air 
are  dissolved  or  absorbed  by  the  water.  Thus  the  oxygen 
which  is  absorbed  in  ordinary  river  water  and  which  serves 
for  the  respiration  of  fishes  is  accounted  for  in  this  way. 
Dalton's  law  might  be  stated  in  another  way  which  may 
help  to  make  this  matter  clearer.  Liquids  absorb  gases  un- 
til the  pressure  of  the  gas  dissolved  in  the  liquid  is  just  the 
same  as  the  pressure  of  that  gas  above  the  liquid.  A  few 
illustrations  may  prove  helpful.  If,  in  the  case  of  an  ordi- 
nary engine  boiler  a  valve  be  opened  in  the  lower  part  of 
the  boiler  where  the  water  is,  the  water  is  forced  out  with 
the  same  pressure  as  the  steam  would  be  forced  out  from  the 
upper  part  of  the  boiler.  That  is  to  say,  the  pressure  in  the 
water  of  the  boiler  is  the  same  as  the  pressure  of  the  steam 
above  that  water.  Or,  to  illustrate  further,  in  a  bottle  not 
quite  filled  with  some  heavily  charged  mineral  water  there  is 
a  certain  amount  of  gas  above  the  liquid.  If  the  stopper 
from  such  a  bottle  should  be  removed  not  only  would  the  gas 
above  the  liquid  be  forced  out,  but  the  gas  dissolved  in  the 
liquid  would  try  to  relieve  itself  of  the  pressure  to  which  it 
has  been  subjected,  and  so  flow  out  of  the  bottle,  frequently 
carrying  bits  of  the  liquid  along  with  it  as  a  froth  or  foam. 
As  soon  as  a  glass  of  heavily  charged  soda-water  is  drawn 
and  placed  on  the  table  to  be  served,  the  (CO2)  gas  which 
was  dissolved  in  the  water,  now  being  relieved  of  the  pres- 
sure of  the  gas  above  it,  leaves  the  water  and  causes  the 
familiar  froth,  or,  as  it  is  called,  the  effervescence  of  that 


THE    UJNGS    AND    RESPIRATION.  221 

liquid.  This  loss  of  gas  in  all  these  cases  would  continue 
until  finally  the  pressure  of  the  gas  in  the  liquid  itself  would 
sink  as  low  as  the  pressure  of  that  gas  in  the  atmosphere 
above  the  liquid,  when  things  would  come  to  a  standstill. 

The  phenomenon  of  boiling  is  a  still  further  illustration 
of  this  same  fact.  As  the  water  becomes  gradually  more 
and  more  heated  the  pressure  of  steam  in  the  liquid  rises 
correspondingly,  until  finally  a  point  is  reached  at  which  the 
pressure  of  the  steam  in  the  liquid  is  a  little  greater  than 
the  pressure  of  the  atmosphere  above  the  liquid.  As  a  re- 
sult of  this  the  water  is  thrown  upward  to  allow  the  steam  to 
escape.  This  throwing  up  of  the  water  is,  of  course,  the 
familiar  boiling  of  the  liquids.  For  this  reason  we  ought  to 
expect  that  water  would  boil  more  quickly  the  lower  the  at- 
mospheric pressure.  Such  is,  of  course,  the  case,  and  water 
will  boil  on  high  mountainous  altitudes  at  very  much  re- 
duced temperatures.  Finally,  it  may  not  be  altogether  out 
of  place  to  call  renewed  attention  to  the  fact  that  such  a  gas 
absorbed  in  or  dissolved  by  a  liquid  is  not  held  in  that  liquid 
in  the  form  of  bubbles,  but  is  thoroughly  dissolved  in  it  and 
to  the  eye  invisible.  Thus,  a  bottle  of  heavily  charged 
mineral  water  will  appear  without  a  bubble  in  it  as  long  as 
it  remains  corked,  and  yet  at  the  moment  of  opening,  in- 
numerable bubbles  will  at  once  form  throughout  the  liquid, 
sometimes  with  such  rapidity  as  to  cause  the  whole  liquid 
to  froth. 

With  this  little  side  excursion  into  the  realm  of  physics, 
let  us  turn  again  to  the  condition  of  things  in  the  lungs 
and  see  the  application  there  of  Dalton's  law. 

A  difficulty  at  once  confronts  us.  The  air  is  not  a 
single  gas.  It  is  made  up  of  at  least  three  gases.  It  con- 
tains about  four-fifths  nitrogen,  one-fifth  oxygen,  and  then 
traces  of  CO2.  The  experiments  of  the  physicist  again 
help  us  out  here,  for  in  all  cases  where  a  liquid  is  subjected 
to  a  mixture  of  gases  each  gas  acts  independently  of  all  the 
others;  that  is,  the  amount  of  one  gas  which  will  be  ab- 
sorbed by  a  liquid  is  not  in  any  way  influenced  by  the 


222  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

presence  of  any  other  gases.  We  have  in  every  case  to  do 
only  with  the  pressure  of  the  one  gas  in  question.  Now, 
one-fifth  of  the  atmosphere  is  oxygen,  four-fifths  nitrogen, 
disregarding  for  the  moment  the  other  ingredients.  As  the 
pressure  of  the  atmosphere  is  fifteen  pounds  to  the  square 
inch,  a  fifth  of  that  is  due  to  oxygen;  that  is,  the  pressure 
of  oxygen  to  the  square  inch  is  three  pounds,  while  the 
pressure  of  the  nitrogen,  the  remaining  four-fifths  of  the 
atmosphere,  is  of  course  four-fifths  of  fifteen  pounds,  or 
twelve  pounds.  In  studying  the  action  of  the  oxygen  in 
the  lung,  we  need  only  to  take  into  account  the  fact  that 
the  oxygen  presses  on  the  blood  in  the  capillaries  with  a 
pressure  equal  to  three  pounds  to  the  square  inch,  and  we 
may,  without  fear  of  any  complications,  entirely  disregard 
the  presence  of  the  other  gases.  For  if  the  blood  should  be 
put  into  a  closed  vessel  and  all  the  nitrogen  of  the  air  in 
that  vessel  be  removed  chemically,  no  difference  would  re- 
sult. In  conformity  with  the  law  of  Dal  ton,  oxygen  will 
be  absorbed  by  the  plasma  until  the  pressure  of  the  oxygen 
in  the  plasma  becomes  the  same  as  the  pressure  of  oxygen 
above  it;  that  is,  three  pounds;  and  the  nitrogen  will  be 
absorbed  by  the  plasma  until  the  pressure  of  nitrogen  in  it 
will  be  equal  to  the  pressure  of  nitrogen  immediately 
above  it. 

So  far  there  would  be  not  one  iota  of  difference  between 
what  happens  to  the  venous  blood  in  the  lung  and  what 
happens  to  the  water  in  a  river.  Both  subjected  to  the 
same  atmosphere  would  dissolve  the  same  proportion  of 
oxygen  and  nitrogen.  Animals  which  have  colorless  blood 
only,  for  instance,  the  oyster  or  the  crayfish,  get  their 
supply  of  oxygen  from  the  amount  of  this  gas  which  the 
water  of  their  blood  will  dissolve.  As  every  one  knows, 
however,  ordinary  water  does  not  dissolve  very  much 
oxygen,  and  fishes  which  are  put  in  an  aquarium  must  have 
the  water  renewed  at  very  frequent  intervals,  as  the  oxygen 
supply  of  the  water  is  rapidly  exhausted.  For  this  reason 
animals  that  can  get  no  other  oxygen  except  that  carried 


THE   LUNGS   AND   RESPIRATION.  223 

by  the  liquid  of  the  blood  are  necessarily  cold-blooded,  and 
frequently  very  sluggish,  much  like  a  fire  which,  devoid  of 
a  good  draft,  would  have  to  burn  slowly  and  smoulder.  But 
in  the  case  of  the  blood  of  all  higher  animals  a  new  factor 
is  added.  This  new  factor  is  the  haemoglobin  contained  in 
the  red  corpuscles.  This  haemoglobin  has  the  chemical 
property  of  combining  with  oxygen  whenever  the  pressure 
of  the  oxygen  is  a  half  pound  or  more,  and  of  giving  up  the 
oxygen  just  as  soon  as  the  pressure  of  oxygen  surrounding 
it  sinks  below  a  half  pound.  This  property  of  haemoglobin 
is  by  no  means  a  unique  one.  There  are  many  chemicals 
which,  under  high  pressure,  will  form  combinations  with 
other  substances,  and  at  lower  pressure  will  again  disunite. 
We  have  here  to  do  not  with  a  mysterious  physiological 
problem,  but  with  a  simple  every-day  chemical  fact. 

THE  EOLE   OF  THE  BED  CORPUSCLES. 

I/et  us  now  see  just  what  role  the  red  corpuscle  with  its 
haemoglobin  plays  in  the  pulmonary  capillaries.  In  a  way 
described  above  the  oxygen  is  absorbed  by  the  plasma  and 
the  oxygen  pressure  in  the  same  will  at  once  begin  to 
rise.  When,  however,  this  pressure  in  the  plasma  rises 
above  a  half  pound  the  haemoglobin  will  at  once  seize  the 
oxygen  absorbed  in  the  plasma  and  unite  chemically  with 
it.  This  oxygen  so  taken  out  of  the  plasma  is,  of  course, 
replaced  at  once  by  fresh  oxygen  which  streams  in  from  the 
outside.  As  the  pressure  of  the  oxygen  in  the  air  is  three 
pounds  to  the  square  inch,  it  will  continue  to  stream  into 
the  plasma  until  the  pressure  there  will  be  three  pounds. 
But  before  the  pressure  reaches  three  pounds,  in  fact,  just 
as  soon  as  it  passes  the  half-pound  limit,  the  haemoglobin  in 
the  red  corpuscles  will  pick  out  the  oxygen  from  the 
plasma,  unite  chemically  with  it,  and  so  prevent  the  pres- 
sure in  the  plasma  from  reaching  three  pounds.  This  will 
go  on  until  finally  all  of  the  haemoglobin  has  united  with 
oxygen;  that  is,  until  all  of  the  haemoglobin  has  been 
changed  into  oxyhaemoglobin.  After  this  point  is  reached 


224  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

the  oxygen  will  continue  to  stream  into  the  plasma  until  the 
pressure  in  the  plasma  reaches  three  pounds,  and  then 
everything  will  come  to  a  standstill.  Of  course  at  this 
juncture  the  blood  is  pushed  onward  into  the  pulmonary 
veins  and  is  as  arterial  blood  sent  back  to  the  left  side  of 
the  heart,  to  be,  of  course,  in  the  lung  replaced  by  fresh 
venous  blood  from  the  pulmonary  arteries. 

By  way  of  summary  the  condition  of  things  in  this 
arterial  blood  as  it  leaves  the  lungs  is  re-stated.  The 
plasma  of  the  arterial  blood  has  oxygen  dissolved  in  it  to 
a  pressure  of  three  pounds  to  the  square  inch,  or  at  least 
not  very  far  from  that.  All  the  haemoglobin  has  been 
changed  into  oxyhaemoglobin,  and  as  this  oxyhsemoglobin 
is  in  the  plasma  surrounded  by  an  oxygen  pressure  of  moi;e 
than  half  a  pound  it  does  not  disunite  with  its  oxygen.  In 
this  condition  of  things  the  blood  is  sent  out  through  the 
arteries  over  the  entire  body  and  finally  reaches  the  capil- 
laries in  the  tissues.  This  is  the  seat  of  the  internal 
respiration. 

THE  PHENOMENA  OF  INTERNAL  EESPIEATION. 

1. — The  Oxygen  Supply.  In  order  here,  also,  to  more 
thoroughly  understand  just  what  takes  place  in  this  gaseous 
interchange,  let  us  picture  the  exact  condition  of  things  in 
the  tissues.  The  arterial  blood,  as  described,  is  in  the  tis- 
sue capillaries.  Just  outside  of  the  capillaries  lies  the 
lymph  which  bathes  the  tissues,  and  in  which  lie  the  live 
cells  of  the  body,  the  units  for  which  the  nourishment  of 
the  blood  and  the  oxygen  which  it  carries  are  intended. 
These  cells  immersed  in  the  lymph  have  a  great  avidity  for 
oxygen,  and  use  it  up  as  fast  as  it  is  carried  to  them.  Stat- 
ing this  in  a  more  scientific  way,  there  is  in  the  lymph, 
bathing  healthy  tissues,  never  much  free  oxygen,  and  of 
course  there  can  then  be  no  oxygen  pressure.  We  have  the 
lymph  with  no  oxygen  pressure  in  it,  separated  from  the 
plasma  of  the  blood  which  has  a  three-pound  pressure,  by 
a  thin  capillary  wall.  It  was  pointed  out  in  discussing 


THE    LUNGS    AND    RESPIRATION.  225 

external  respiration  that  the  presence  of  such  a  membrane 
does  not  in  any  way  hinder  gaseous  interchange,  and  so  we 
may  again  imagine  the  plasma  in  the  capillaries  in  immedi- 
ate contact  with  the  lymph  bathing  the  tissues.  As  there 
is  a  three-pound  pressure  in  the  plasma,  and  no  pressure  in 
the  lymph,  the  oxygen  will  stream  from  the  plasma  into  the 
lymph,  just  as  in  opening  a  bottle  of  mineral- water  where 
the  pressure  of  the  gas  in  the  bottle  is  much  greater  than 
the  pressure  of  that  gas  on  the  outside  of  the  bottle,  the 
gas  will  stream  out  into  the  air  surrounding  the  bottle. 
This  streaming  of  oxygen  out  of  the  plasma  will  continue , 
until  finally  the  oxygen  pressure  of  the  plasma  sinks  to  a 
half  pound. 

It  will  be  noticed  that  up  to  this  point  the  red  corpuscles 
have  taken  no  part  at  all  in  the  process  of  the  gaseous 
interchange,  but  as  soon  as  the  oxygen  pressure  in  the 
plasma  sinks  to  or  below  a  half  pound  the  haemoglobin  is 
no  longer  able  to  remain  united  with  the  oxygen,  but  dis- 
associates. The  oxygen  so  liberated  from  the  oxy haemo- 
globin flows  into  the  plasma  with  which  it  is  surrounded, 
and  from  the  plasma  in  turn  the  oxygen  streams  into  the 
lymph.  This  will  continue  until  finally  all  of  oxyhaemo- 
globin  has  been  disunited,  and  until  almost  all  the  oxygen 
from  the  plasma  has  streamed  into  the  lymph.  The  oxygen 
does  not  accumulate  in  the  lymph,  for  in  the  tissues  this 
gas  is  used  up  almost  as  fast  as  it  is  brought,  and  so  the 
oxygen  pressure  in  the  lymph,  in  spite  of  the  amount  of 
gas  carried  to  it,  remains  practically  nothing.  The  fact  that 
the  oxygen  does  not  accumulate  but  is  used  up  as  fast  as  it 
is  brought  explains  why  it  is  impossible,  even  for  a  very 
short  interval  of  time,  to  be  deprived  of  air.  It  takes  but 
a  minute  or  more  of  a  loss  of  air  to  induce  the  fatal  effects 
of  suffocation.  About  the  instant  when  all  the  oxygen  has 
been  taken  out  of  the  blood,  this /is  pushed  into  the  veins 
and  sent  back  to  the  heart  for  a  fresh  supply. 

Here,  also,  by  way  of  summary,  the  condition  of  things 
in  the  venous  blood  as  it  leaves  the  tissues  is  re-stated. 


226  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

The  oxygen  pressure  in  the  plasma  is  very  low,  less  than  a 
half  pound.  For  this  reason  all  of  the  oxyhsemoglobin  has 
been  disassociated  and  the  haemoglobin  only  is  left.  Thus 
it  will  be  seen  that  the  reason  why  the  blood  does  not  give 
off  any  of  its  oxygen  until  it  reaches  the  tissues  is,  that  all 
through  the  arteries  the  pressure  of  the  oxygen  in  the 
plasma  remains  constant,  but  sinks  below  the  critical  half 
pound  limit  in  the  capillaries  only.  In  the  chapter  on  Blood 
it  was  stated  that  by  far  the  larger  amount  of  oxygen  was 
carried  by  the  corpuscles  and  a  relatively  small  amount 
only  by  the  plasma.  The  proportion  is  given  by  some  physi- 
ologists as  ten  to  one,  but  while  this  is  true,  it  will  be 
noticed  from  the  preceding  that  the  plasma  and  the  oxygen 
dissolved  in  it,  play  a  most  important  role  in  the  process  of 
respiration. 

2. — The  Elimination  of  the  Carbon  Dioxide.  But  the 
preceding  is  only  half  of  the  story.  In  the  process  of  res- 
piration not  only  is  oxygen  taken  up  in  the  lungs  and 
carried  to  the  tissues,  but  carbon  dioxide  is  picked  up  in  the 
tissues  and  eliminated  from  the  lung.  There  now  remains 
a  more  detailed  description  of  the  actual  manner  in  which 
this  carbon  dioxide  is  picked  up  in  the  capillaries  and  finally 
thrown  out  in  the  lungs. 

Carbon  dioxide  is  produced  when  any  tissue  in  the  body 
is  in  action.  It  is  the  result  of  activity  of  the  brain  no  less, 
probably,  than  that  of  the  muscle,  but  on  account  of  the 
difficulty  of  observation,  the  finer  details  as  to  the  sources 
of  the  carbon  dioxide  have  been  worked  out  for  the  muscles. 
In  the  chapter  on  the  nutrition  of  the  muscle  it  was 
pointed  out  that  the  food  brought  by  the  plasma  and  the 
oxygen  brought  by  the  blood  were  built  up  into  living 
muscle.  It  is  important,  therefore,  to  bear  in  mind  that  as 
far  as  we  now  know  the  oxygen  carried  to  the  muscles  is 
not  used  in  burning  them,  as  is  so  frequently  stated,  but  is 
used  in  building  them  up.  Consequently  the  carbon  dioxide 
does  not  arise  as  the  immediate  product  of  combustion  due 
to  the  arrival  of  the  oxygen  in  the  muscles.  In  the  case 


THE   LUNGS   AND    RESPIRATION.  227 

of  the  tissues  there  is  no  analogy  with  the  stove.  In  the 
stove  the  fuel  and  the  entering  oxygen  at  once  combine, 
combustion  occurs,  and  carbon  dioxide  is  the  result.  But 
in  the  muscle  the  food  and  the  oxygen  are  not  at  once 
burned,  but  are  in  a  way,  entirely  unknown  to  us,  built 
into  living  tissue,  much  as  in  the  manufacture  of  gunpow- 
der all  the  various  elements  are  built  up  without  any  com- 
bustion taking  place,  until  later,  when  it  is  purposely 
ignited.  Upon  the  ignition  of  the  gunpowder  it  at  once 
breaks  up  into  a  number  of  burned  products,  not  the  least 
one  of  which  is,  by  the  way  here,  carbon  dioxide.  The 
carbon  dioxide  in  the  muscles  is  due  to  a  disintegration  of 
parts  of  the  muscle  substance  itself.  Thus,  the  amount  of 
carbon  dioxide  formed  in  the  muscles  will  vary  directly 
with  the  amount  of  muscular  work  done  in  the  same  way 
as  the  amount  of  smoke  in  battle  will  vary  directly  with  the 
number  of  shots  fired. 

To  show  that  carbon  dioxide  may  be  formed  in  a  muscle 
when  there  is  no  oxygen  present,  the  following  experiment 
will  suffice:  If  a  living  muscle,  say  from  a  frog,  be  put  in 
a  closed  case  and  all  the  oxygen  withdrawn  it  will,  when 
properly  stimulated,  contract  as  usual,  and  the  production 
of  CO 2  follows.  In  fact,  the  absence  of  even  traces  of  oxy- 
gen does  not  seriously  affect  the  muscle  for  a  while,  but  it 
keeps  on  contracting  for  some  time  and  finally  becomes 
exhausted  because  its  reserve  material,  not  being  replen- 
ished, is  gradually  used  up.  If  the  CO2  in  the  muscle  were 
the  result  of  the  direct  burning  of  the  oxygen  as  soon  as  it 
enters  the  muscle,  such  an  experiment  with  such  results 
would  be  impossible. 

As  all  living  cells  are  continually  at  work,  if  not  in 
giving  rise  to  motion  at  least  in  producing  heat  and  in 
keeping  up  the  bodily  temperature,  so  there  is  going  on 
continually  in  our  tissues  a  production  of  CO2.  This  gas 
will  at  once  be  absorbed  by  the  surrounding  lymph  in  con- 
formity with  the  law  of  Daltoii.  Thus  there  will  come  to 
be  in  the  lymph  quite  a  little  CO2  pressure.  In  the  blood 


228  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

of  the  capillaries  there  is  no  CO2,  as  the  arterial  blood  just 
coming  from  the  lungs  has  practically  no  CO2  in  it  (the  air 
itself  having  practically  none) ,  so  in  further  conformity  with 
Dalton's  law  the  CO2  will  stream  into  the  plasma  of  the 
blood,  the  walls  of  the  capillaries  being  entirely  disre- 
garded. But,  as  everyone  knows,  ordinary  water  (and 
plasma  is  mainly  water)  cannot  absorb  very  much  CO2  at 
ordinary  pressures.  When  we  do  want  the  water  to  absorb 
larger  quantities,  as  in  the  manufacture  of  soda-water,  such 
water  must  be  subjected  to  very  high  gas  pressures.  The 
difficult  problem  therefore  presents  itself  of  explaining  how 
the  large  amounts  of  CO2  which  are  breathed  out  at  each 
breath  are  really  carried  by  the  blood.  In  the  first  place, 
the  corpuscles  of  the  blood  do  not  carry  CO2.  Blood  with 
the  corpuscles  left  in  it  carries  a  little  more  CO2  than  when 
the  corpuscles  are  taken  out,  but  this  is  due  to  the  fact 
that  the  corpuscles  themselves  are  soaked  with  plasma,  and 
the  plasma,  like  any  liquid,  will  absorb  certain  amounts  of 
CO2.  We  must,  therefore,  look  to  the  plasma  itself  as  the 
carrying  agent  of  this  gas.  And  yet  by  experiment  it  can 
be  conclusively  shown  that  we  breathe  out  much  more  CO2 
at  each  breath  than  could  be  absorbed  by  the  plasma  in  that 
time.  In  short,  while  some  of  the  CO2  is  absorbed  by  the 
plasma,  some  of  it  must  be  held  in  chemical  combination. 
Now  just  what  this  chemical  combination  is,  physiologists 
can  not  yet  determine.  It  seems,  however,  highly  probable 
that  as  the  blood  is  normally  alkaline,  much  of  the  CO2  in 
the  capillaries  of  the  tissue  unites  with  the  alkaline  sub- 
stances of  the  blood  and  forms  carbonates.  To  .even  the 
most  elementary  student  in  chemistry  the  following  expla- 
nation, though  given  unfortunately  in  technical,  chemical 
terms,  will  seem  very  clear:  There  are  contained  in  ven- 
ous blood  certain  quantities  of  (Na2  CO3)  sodium  carbon- 
ate. When  a  liquid  containing  Na2  CO3  has  added  to  it 
CO2  gas,  it  forms  a  new  combination  with  this  gas,  and 
there  results  Na  H  CO3,  sodium  bicarbonate.  This  Na  H 
CO 3  is  possibly  more  familiar  to  us  as  ordinary  baking- 


THE    LUNGS    AND    RESPIRATION.  229 

soda.  As  this  substance  is  very  soluble  in  water,  and  con- 
sequently soluble  in  blood  plasma,  large  quantities  of  it 
could  be  easily  carried  in  solution. 

By  way  of  summary  what  has  occurred  in  the  capillaries 
of  the  tissue  may  be  re-stated  thus:  First,  the  CO2  has 
resulted  from  an  actual  breaking  down  of  the  living  tissue. 
Second,  from  the  tissue  it  has  been  absorbed  by  the  lymph 
which  bathes  the  tissues.  Third,  from  the  lymph  it  streams 
into  the  blood  plasma.  Here  a  certain  quantity  of  it  is  car- 
ried, merely  absorbed  or  dissolved  in  it.  Fourth,  in  the 
plasma  a  larger  quantity  of  the  CO2  enters  into  chemical 
combination  with  some  of  the  alkaline  substances,  possibly 
Na2  CO 3,  (sodium  carbonate,)  and  forms  Na  H  CO3  (so- 
dium bicarbonate) .  This  sodium  bicarbonate  is  easily  sol- 
uble in  the  plasma,  and  so  in  solution  is  carried  lungward 
in  the  venous  stream. 

3. — The  Elimination  of  Co 2  in  the  Lungs.  The  final 
scene  in  this  drama  of  the  respiration  is,  of  course,  the  elimi- 
nation of  this  CO2  from  the  blood  into  the  lungs.  When 
the  venous  blood  reaches  the  pulmonary  capillaries  the  CO2 
dissolved  in  the  plasma  of  the  blood  at  once  begins  to  pass 
out  of  the  blood  into  the  air,  since  the  pressure  of  the  CO2 
in  the  air  is  practically  nothing.  This  streaming  out  of 
the  CO2  is,  therefore,  in  regular  obedience  to  the  law  of 
Dalton.  In  this  way  all  the  CO2  merely  dissolved  in  the 
plasma  is  finally  eliminated.  If  venous  blood  were  put 
under  the  receiver  of  an  air  pump  and  the  air  above  it 
then  exhausted,  it  would  be  possible  to  pump  out  of  the 
blood  practically  all  of  the  CO2  absorbed  in  it.  This  por- 
tion of  the  gas  then  presents  no  difficulty.  It  streams  out 
into  the  lung  for  the  same  reason  that  the  bubbles  of  gas 
stream  out  of  a  bottle  of  mineral-water  when  that  mineral- 
water  conies  in  contact  with  the  air.  But  the  difficulty 
presents  itself  when  we  try  to  explain  in  what  manner  the 
CO2,  which  is  chemically  combined  in  the  sodium  salt,  is 
liberated. 


230  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

It  was  stated  that  ordinary  Na  H  CO3  is  the  familiar 
baking-soda.  Baking-soda  is  used  to  get  the  CO2  gas 
which  is  liberated  from  it  when  sour  milk,  or  for  that 
matter  any  acid  is  poured  over  it.  Everybody  is  familiar 
with  the  fact  that  if  baking-soda  be  taken  and  anything 
sour  be  added  to  it,  it  begins  to  froth  and  bubble,  and  large 
quantities  of  CO2  gas  stream  out.  This  is  exhibited 
especially  well  in  the  common  Seidlitz  powder.  Here 
Na  H  CO 3  and  some  acid  (tartaric,  etc.)  are  mixed  to- 
gether, as  a  result  of  which  the  liquid  begins  to  effervesce 
very  strongly.  The  addition  of  some  acid  to  the  soda  has 
liberated  large  quantities  of  CO2  gas.  Common  soda-water 
(which  is  but  water  charged  heavily  with  CO2)  derives 
its  name  from  the  fact  that  formerly  this  CO2  gas  was  de- 
rived from  ordinary  soda  by  pouring  acids  over  it.  Now  it 
is  highly  probable  that  the  chemical  substance  in  venous 
blood  carrying  the  CO2  in  combination,  is  soda,  and  to 
liberate  the  CO2  so  contained  some  acid  must  be  present. 
The  acid  in  the  case  of  the  lung  is  oxy haemoglobin.  While 
haemoglobin  itself  is  very  faintly  acid,  oxyhaemoglobin  is 
much  more  markedly  acid.  Although  this  oxyhaemoglobin 
is  not  acid  enough  to  appear  sour  to  the  taste,  it  is  acid 
enough  to  act  upon  the  soda  dissolved  in  the  plasma  and 
liberate  the  CO2.  It  is  at  once  apparent  that  this  oxyhaemo- 
globin, being  formed  in  the  lungs,  was  not  present  in 
venous  blood.  Consequently  there  was  no  liberation  of  the 
CO2  in  the  veins,  but  arrived  at  the  capillaries  of  the  lungs 
the  haemoglobin  becomes  converted  into  oxhyaemoglobin, 
which,  acid  in  its  nature,  at  once  reacts  upon  the  soda  in 
the  plasma  and  liberates  from  this  the  CO2,  which  then 
streams  out  into  the  lungs. 

Thus  it  will  be  seen  that  the  CO2  is  carried  in  two 
ways ;  one  part  of  it  dissolved  in  the  plasma,  which  when  it 
arrives  at  the  lungs  passes  from  the  plasma  into  the  air  of 
the  alveoli  in  obedience  to  the  general  law  of  gases;  the 
other  part  united  chemically  with  substances,  sodium  car- 
onate  (Na2  CO3)  in  venous  blood  to  form  sodium  bicar- 


THE   LUNGS   AND   RESPIRATION.  231 

bonate  (Na  H  CO3),  and  so  dissolved  and  carried  to  the 
lung,  where  it  is  liberated  by  the  acid  action  of  the 
oxy haemoglobin.  It  will  thus  be  seen  that  even  the  ap- 
parently simple  phenomena  of  the  gaseous  interchanges  in 
the  blood,  in  lungs  and  capillaries  are  carried  on  in  strict 
obedience  to  known  physical  and  chemical  laws  and 
arranged  with  a  nicety  which  is  certainly  striking. 

So  far  nothing  has  been  said  of  the  nitrogen  of  the 
atmosphere.  This  gas  seems  to  play  no  part  whatever  in 
the  respiration  of  the  body.  It  is,  of  course,  carried  by  the 
blood,  just  as  any  other  gas,  but  is  not  used  up  by  the 
tissues,  and  so  serves  only  to  help  maintain  the  pressure  of 
internal  liquids  against  the  air. 

THE  INNERVATION  OF  THE  RESPIRATORY  SYSTEM. 

The  nerves  which  are  immediately  concerned  in  the 
movements  of  respiration  are  the  motor  nerves,  going  to  the 
intercostal  muscles  and  to  the  diaphragm,  and  for  forced 
expirations  to  the  muscles  of  the  abdominal  wall.  All  these 
motor  nerves  come  from  the  spinal  cord,  but  take  their 
origin  further  up  in  the  medulla.  Hence,  cutting  the 
upper  end  of  the  spinal  cord  at  once  destroys  the  power  to 
breathe,  because  it  cuts  through  the  path  of  these  motor 
nerves. 

1. — The  Respiratory  Center.  These  nerves,  however, 
are  but  the  mere  avenues  along  which  the  impulses  to 
breathe  are  carried.  The  impulses  themselves  originate  in 
the  respiratory  center,  which  lies  in  the  medulla  just  at  the 
end  of  the  calamus  scriptorius  in  the  fourth  ventricle. 
(See  Brain.)  It  seems  to  be  a  paired  center,  for  when  the 
medulla  is  cut  through  the  middle  line  the  breathing  on 
each  side  continues,  but  an  injury  to  the  center  itself  at 
once  stops  breathing.  As  we  usually  think  an  animal  is  dead 
as  soon  as  it  stops  breathing,  this  point  has  been  called  the 
"vital  point."  A  rather  horrible  example  of  an  injury  to 
this  center  is  the  execution  by  hanging.  In  this  form  of 
taking  life  the  odontoid  process  of  the  axis  is  pulled  out  of 


232  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

its  accustomed  place  by  the  drop  of  the  body  and  goes 
crushing  through  the  medulla.  As  the  respiratory  center 
lies  just  at  this  point  it  is  destroyed,  and  an  immediate  par- 
alysis of  all  the  muscles  of  respiration  ensues.  In  conse- 
quence of  this  the  criminal  dies  by  suffocation,  not  being 
able  to  get  more  air.  Such  a  displacement  of  the  neck  is 
called  '  'breaking  of  the  neck. ' '  It  is  tolerably  easy  to  locate 
this  point  by  introducing  sharp-pointed  needles  into  the 
medulla.  A  point  is  soon  found  which,  upon  being  pierced 
results  at  once  in  a  respiratory  paralysis,  and  the  position 
of  this  point  in  the  floor  of  the  fourth  ventricle  has  just  been 
noted.  We  must  look  to  this  center,  therefore,  as  the  source 
of  our  respiratory  impulses. 

The  question  at  once  arises,  what  causes  this  center  to 
send  out  impulses  along  the  motor  nerves  just  mentioned? 
A  few  simple  experiments  serve  to  materially  clarify  this. 
If  an  individual  breathes  very  rapidly  and  deeply,  and  so 
gets  into  his  lungs,  and  consequently  into  his  blood,  in- 
creased amounts  of  oxygen,  the  center  becomes  quiescent, 
and  for  a  little  while  there  is  no  tendency  or  temptation  to 
breathe.  This  might  seem  to  show  that  it  is  the  absence 
of  sufficient  oxygen  which  normally  stimulates  the  center, 
for  as  soon  as  the  blood  is  richly  supplied  with  oxygen  by 
taking  repeated  deep  breaths,  the  center  becomes  inactive. 
On  the  other  hand,  if  the  supply  of  air  be  cut  off  and  the 
blood  in  the  body  becomes  strongly  venous,  the  center  be- 
comes more  and  more  irritable,  sends  out  stronger  and 
stronger  impulses  to  breathe,  until  finally  the  impulses  be- 
come so  strong  and  scattered  as  to  produce  convulsions.  In 
such  venous  blood  there  is  still  a  little  oxygen,  but  much 
carbon  dioxide,  and  the  opinion  has  been  advanced  that  it 
is  not  so  much  the  lack  of  oxygen  as  it  is  the  presence  of 
carbon  dioxide  that  stimulates  the  center.  Other  physiol- 
ogists, to  reconcile  both  views,  combine  the  two  notions 
and  state  that  the  absence  of  oxygen,  as  well  as  the  pres- 
ence of  carbon  dioxide,  serve  to  irritate  and  stimulate  the 
center  to  action.  It  seems,  however,  difficult  to  conceive 


THE   LUNGS   AND    RESPIRATION.  233 

how  a  thing  which  is  absent  may  serve  as  a  positive  stimu- 
lus. This  savors  just  a  little  of  a  mental  absurdity.  It  is 
perfectly  conceivable  how  the  presence  of  the  carbon  diox- 
ide in  blood  might  stimulate  the  center,  but  experiments 
have  been  made  by  passing  different  kinds  of  blood  heavily 
charged  with  carbon  dioxide  through  the  center,  and  yet 
the  center  has  failed  to  be  materially  stimulated  by  these 
large  quantities  of  that  gas.  Of  late,  therefore,  physiolo- 
gists have,  looked  elsewhere  for  the  substance  in  question. 
Quite  a  suggestive  experiment  was  made  when  blood 
which  had  just  passed  through  a  severely-exercised  muscle 
was  then  injected  into  the  arteries  which  traverse  the  respir- 
atory center.  A  very  violent  stimulation  was  at  once  the 
result.  This  would  seem  to  indicate  that  when  tissues  such 
as  the  muscle  are  hard  at  work  there  is  a  production  of  waste 
products  of  some  kind  which  act  as  a  powerful  irritant  to 
this  center.  This  irritating  waste  product  may  possibly  be 
eliminated  in  the  lungs,  or  possibly  destroyed  when  the 
blood  becomes  arterial,  either  case  explaining  why  increased 
breathing  will  serve  to  lessen  the  stimulating  effect  of  this 
substance.  If,  for  instance,  the  blood  does  not  succeed  in 
passing  to  the  lungs  rapidly  enough,  this  irritating  waste 
product  accumulates  in  the  blood,  and  so  stimulates  the 
center  to  more  and  more  activity.  If,  on  the  other  hand, 
by  the  process  of  breathing  this  substance  is  eliminated, 
either  through  the  lung  or  destroyed  in  the  blood  as  soon 
as  it  becomes  arterial,  we  can  understand  why  when  such 
blood  passes  through  the  center  the  center  remains  quiet 
and  inactive.  This  will  explain  why  there  are  no  respira- 
tory movements  before  birth,  for  at  this  time  the  blood 
stream  is  richly  supplied  with  oxygen  from  the  maternal 
wall.  This  waste  product  is  given  no  chance  to  accumu- 
late in  the  blood,  but  by  the  oxygen  from  the  placenta  it  is 
continually  removed.  On  account  of  this  the  center  is  not 
at  all  stimulated  and  so  remains  perfectly  dormant,  sending 
out  not  a  single  impulse  to  breathe.  However,  at  the  mo- 
ment of  birth,  when  the  circulation  with  the  placenta  is  cut 


234  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

off,  and  the  supply  of  oxygen  becomes  short  and  this  waste 
product,  therefore,  accumulates,  the  center  becomes  at  once 
irritated  by  it  to  a  greater  and  greater  extent,  until  finally 
the  movements  of  respiration  are  ushered  in. 

That  condition  in  which  the  blood  is  so  richly  supplied 
with  oxygen  that  there  is  no  tendency  to  breathe,  is  called 
apnce.  The  condition  in  which  the  center  is  normally  stim- 
ulated is  called  eupnce,  while  finally  that  condition  in  which 
there  is  not  an  adequate  supply  of  oxygen,  and  which  leads 
to  the  phenomena  of  suffocation  and  to  the  convulsions 
accompanying  the  same  is  called  dyspnce.  From  these  defi- 
nitions it  will  be  seen  that  the  condition  of  respiration  be- 
fore birth  is  that  of  apnce.  But  it  not  infrequently  happens 
that  even  before  birth  the  circulation  with  the  placenta  is 
interrupted,  the  oxygen  supply  of  the  foetus  is  cut  off,  and 
so  dyspnce  results,  which  may  lead  to  real  active  respiratory 
movements. 

As  the  tissues  are  always  in  action  and  as  this  irritating 
substance,  therefore,  must  continually  be  forming,  we  are 
forced  to  believe  that  this  center  must  be  continually  irri- 
tated by  this  substance.  The  question  then  at  once  arises, 
why  this  center  which  is  being  constantly  and  without  in- 
terruption irritated  will  give  rise  to  impulses  which  are 
periodic.  Why  would  not  a  continued  stimulation  of  this 
center  produce  a  tetanus  just  in  the  same  way  as  a  continued 
stimulation  of  the  nerve  of  the  muscle  would  produce  a  con- 
tinued tetanic  contraction?  This  is  explained  by  supposing 
that  there  is  a  kind  of  resistance  in  this  center,  and  that  an 
impulse  does  not  result  until  this  intrinsic  resistance  to  act 
is  overcome. 

This  center  is,  using  a  rather  far-fetched  metaphor,  a 
kind  of  intermittent  spring.  Such  an  intermittent  spring 
will  discharge  its  waters  periodically  in  spite  of  the  fact 
that  its  supply  flows  into  it  at  a  constant  and  uniform  rate. 
So  in  this  center.  The  stimuli  from  this  irritating  substance 
normally  found  in  venous  blood,  and  possibly,  as  was  stated, 
a  waste  product  of  the  active  tissues,  keep  flowing  in,  ac- 


THE    LUNGS   AND    RESPIRATION.  235 

cumulating  their  force,  so  to  speak,  until  finally  such  stim- 
uli give  rise  to  a  respiratory  impulse.  Or,  to  take  another 
illustration.  We  may  imagine  a  box,  the  bottom  of  which  is 
held  in  place  by  a  spring.  If,  now,  water  be  poured  into  this 
box  and  the  spring  have  an  appreciable  amount  of  strength , 
it  will  not  at  once  drop,  but  the  water  will  accumulate  in 
the  box,  rise  to  a  higher  and  higher  level,  until  finally  the 
weight  of  the  water  in  the  box  will  become  greater  than  the 
strength  of  the  spring  supporting  the  bottom,  when  the 
bottom  will  drop  out,  and  the  water  flow  out  with  one 
gush.  As  soon  as  the  vessel  has  thus  emptied  itself  the 
spring  again  pushes  the  bottom  in  place,  and  the  process 
repeats  itself.  Here,  too,  we  see  how  a  source  that  is  con- 
stant is  changed  into  an  effect  which  is  periodical. 

2. — Nervous  Control  of  the  Respiratory  Center.  But  this 
center  reflexly  stimulated  by  the  blood  which  traverses  it, 
may  be  controlled  within  certain  limits  by  nerves  going 
to  it. 

(1)  Those  nerves  from  the  brain  which  are  under  the 
control  of  the  will  reach  it,  and  every  one  is  familiar  with 
the  fact  than  within  a  wide  range  he  is  able  to  control  his 
movements  of  respiration,  but  that  as  soon  as  this  range  is 
passed  the  movements  go  on  independently  of  the  will. 

(2)  Sensory  nerves  of  the  body  which,  when  violently 
stimulated,   affect    this    center.     Thus,   excessive    pain   in 
almost  any  region  of  the  body  at  once  influences  the  rate  of 
breathing. 

(3)  The  most  important  influences  reaching  this  center 
come  from  the  sensory   nerves   of  the  lung  itself.     These 
sensory  nerves  run  in  the  large  vagus  trunk. 

That  these  sensory  nerves  play  a  most  important  role  in 
controlling  the  center,  may  be  understood  from  the  follow- 
ing experiment:  If  the  vagus  on  one  side  be  cut,  no  marked 
effect  follows;  but  cutting  both  vagi,  there  at  once  results 
a  very  much  slowed  breathing.  The  number  of  breaths  may 
sink  to  one-fourth,  or  even  one-sixth  of  the  normal.  The 


236  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

individual  breaths  are,  however,  deeper.  If,  now,  the  cen- 
tral ends  of  the  vagi,  that  is  those  connected  with  the  brain, 
be  stimulated  with  electrical  stimuli,  the  number  of  breaths 
begins  to  rise  to  the  normal;  Here  is,  of  course,  an  evident 
control  of  the  respiratory  movements.  If  these  vagi  are  then 
excessively  stimulated  there  ensues  sometimes  a  relaxation 
of  the  respiratory  muscles,  that  is  a  passive  expiration; 
at  other  times  a  standstill  of  the  chest  and  lungs  in  the 
position  of  an  inspiration,  in  which  the  respiratory  muscles 
are  in  a  state  of  tetanic  contraction.  Here  we  have  then 
apparently  a  double  effect;  sometimes  relaxation,  sometimes 
greater  contraction.  This  double  effect  shows  that  the  vagi 
have  two  kinds  of  nerve  fibres  in  them  going  from  the  lungs 
to  the  center.  First,  those  that  stimulate  the  center  to 
greater  respiratory  exertion;  and,  secondly,  those  that  tend 
to  inhibit  the  center. 

The  rather  interesting  question  now  presents  itself:  Un- 
der what  circumstances  does  each  of  the  nerves  act  ?  The 
solution  of  this  question  is  probably  found  in  the  following 
experiment:  If  the  lung  of  an  animal  whose  chest  has  just 
been  opened,  be  forcibly  distended  by  pressing  air  into  it, 
there  is  at  once  developed  a  strong  desire  on  the  part  of 
the  animal  to  breathe  out.  An  expiration  is  induced.  If, 
on  the  other  hand,  the  air  be  sucked  out  of  the  lung  and 
the  lung  so  tend  to  collapse,  there  at  once  follows  a  strong 
inclination  for  an  inspiration.  In  other  words,  when  the 
lung  expands  the  center  is  inhibited,  breathing  movements 
stop,  and  the  muscles  relax.  But  the  lung  expands  in  an 
inspiration,  consequently  an  inspiration  induces  an  ex- 
piration. But  in  an  expiration  the  lung  is  compressed,  and 
this  compression  of  the  lung  stimulates  the  center  to  act 
more  energetically;  that  is,  the  center  tends  to  breathe, 
but  actively  breathing  means  to  inspire.  Thus  the  ex- 
piration serves  to  induce  an  inspiration.  We  find,  then,  in 
these  nerves  a  kind  of  self-regulating  arrangement  which 
stated  again  is  as  follows:  When  the  center  sends  an  im- 
pulse to  the  muscles  of  respiration  and  the  chest  is  thus 


THE    LUNGS    AND    RESPIRATION.  237 

enlarged,  the  lung  is  correspondingly  expanded.  But  such 
an  expansion  of  the  lung  at  once  affects  those  sensory 
nerves  in  it  which,  when  stimulated,  inhibit  the  center; 
that  is,  cause  it  to  stop.  So,  as  the  inspiration  proceeds 
and  the  lungs  expand  more  and  more  these  nerves  are  more 
and  more  stimulated,  the  center  is  more  and  more  in- 
hibited, and  is  finally  brought  to  a  standstill.  As  soon  as 
this  happens  the  muscles  of  respiration  relax  and  the  chest 
collapses  of  its  own  accord;  that  is,  a  passive  expiration 
follows.  But  in  this  passive  expiration  the  lung  is  com- 
pressed, and  this  compression  of  the  lung  affects  the  second 
pair  of  sensory  fibres  which  serve  to  stimulate  the  center  to 
greater  activity.  Thus,  as  the  lungs  collapse  more  and 
more,  these  stimuli  become  stronger  and  stronger,  and  so 
finally  arouse  the  center  to  a  renewed  contraction. 

(4)  In  addition  to  these  two  sensory  nerves,  which 
in  the  manner  just  indicated  so  materially  influence  the 
activity  of  this  center,  there  is  one  additional  nerve  which 
exercises  a  marked  effect.  This  is  the  nerve  which  goes  to 
the  larynx.  This  nerve  when  stimulated,  strongly  inhibits 
the  center,  and  so  tends  to  make  an  inspiration  impossible. 
As  this  nerve  is  no  doubt  stimulated  in  the  varying  acts  of 
swallowing,  singing,  talking,  and  so  on,  there  seems  some 
reason  for  this  arrangement.  Thus,  in  the  act  of  swallow- 
ing the  center  is  inhibited,  and  so  the  possibility  of  choking 
is  materially  reduced,  while  in  the  act  of  talking  or  singing 
stimulation  of  this  nerve  tends  to  check  the  rate  of  breath- 
ing, a  circumstance  which  materially  helps  to  sustain  the 
voice. 

When  all  these  rather  remarkable  niceties  in  the  nervous 
control  of  the  movements  of  respiration  are  stated,  there  yet 
remains  much  that  requires  further  investigation,  and  it  is 
possible  that  the  researches  of  the  immediate  future  may 
materially  modify  and  clarify  our  present  knowledge  of  this 
subject. 


238  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

Those  modified  forms  of  breathing  familiar  to  us  all  as 
sneezing  or  coughing,  may  be  so  easily  investigated  by 
each  student  for  himself  that  a  further  description  of  them 
is  here  deemed  unnecessary. 


CHAPTER  X. 


THE    LARYNX    AND    THE    PRODUCTION    OF 
ARTICULATE  SPEECH. 

The  only  property  which  man  possesses  par  excellence 
to  the  exclusion  of  all  other  animals  is  that  of '  articulate 
speech.  The  voice  is  something  which  belongs  to  the 
human  larynx  alone.  Many  of  the  lower  animals  are  able 
to  produce  characteristic  sounds,  and  these  sounds  some- 
times, as  in  the  case  of  birds,  may  extend  through  quite  a 
wide  scale  and  be  of  a  complicated  character;  but  it  goes 
without  question  to  say  that  they  possess  none  of  the  real 
peculiarities  of  articulate  speech.  The  human  voice  con- 
sists of  sounds  which  are  produced  by  the  vibrations  of  two 
elastic  bands  called  the  vocal  cords  placed  in  the  voice- 
box.  This  voice-box,  or  larynx,  is  really  no  more  than  a 
dilatation  of  the  upper  portion  of  the  trachea  so  arranged 
with  a  series  of  cartilage  as  to  enable  the  air  driven  through 
it  to  set  the  vocal  cords  in  vibration.  The  consideration 
of  the  voice  immediately  after  the  subject  of  respiration,  is 
based  upon  its  somewhat  secondary  connection  with  the 
trachea  and  lungs.  Fundamentally  the  physiology  of  res- 
piration and  that  of  articulate  speech  have  nothing  in 
common. 

The  vocal  cords  vibrating  alone  would  produce  but 
feeble  sounds  quite  different  from  the  ordinary  sounds  of 
the  voice.  The  vibrations  of  the  vocal  cords  are,  there- 
fore, strengthened  by  resonance  cavities,  like  the  vibrations 
of  a  violin  string  are  very  integrally  strengthened  by  the 
resonance  of  the  violin  frame  underneath,  or  as  the  note  of 
an  organ  pipe  is  very  dependent  indeed  upon  the  resonance 
cavity  in  the  long  tube  of  the  pipe  in  question.  The  reso- 
nance cavities  for  the  vocal  cords  are  the  larynx  itself,  the 

(239) 


240  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

throat,  the  mouth,  and  in  the  production  of  some  sounds 
even  the  nose.  By  changing  the  relative  dimensions  of 
these  resonance  cavities  the  quality  of  the  individual  sounds 
of  the  voice  may  be  much  varied,  just  as  the  player  on  the 
sliding  trombone  varies  his  notes  by  varying  the  relative 
lengths  of  the  resonance  cavities  in  his  instrument.  The 
pitch  of  the  voice  will  be  dependent  upon  the  length  and 
tension  of  these  vocal  cords,  just  as  the  pitch  of  a  piano 
string  is  dependent  upon  its  length  and  tension,  while  the 
loudness  'will  depend  upon  the  strength  with  which  the 
vocal  cords  are  made  to  vibrate. 

We  have  now  to  consider  the  anatomical  arrangement 
af  the  larynx  by  which  the  vibration  of  the  cords  and  the 
production  of  the  voice  is  effected. 

THE  ANATOMY  OF  THE  LAETNX. 

The  larynx  is  the  expanded  upper  portion  of  the  trachea. 
It  consists  of  three  main  cartilages,  the  general  arrange- 
ment of  which  is  about  as  follows:  At  the  base  of  the 
larynx  is  the  cricoid  cartilage.  This  cartilage  entirely  sur- 
rounds the  base  of  the  larynx  like  a  ring  surrounds  a  finger. 
This  cricoid  cartilage  actually  resembles  in  its  shape  a  sig- 
net ring,  the  signet  of  which  is,  however,  towards  the  back, 
and  the  band  of  the  ring  forwards.  This  band  may  be  felt 
by  pressing  the  finger  hard  against  the  base  of  the  larynx 
in  front.  Placed  upon  the  band  of  this  ring,  that  is, 
towards  the  front  of  the  trachea,  is  the  thyroid  cartilage. 
This  cartilage  really  consists  of  two  cartilages  which  meet 
in  front.,  leaving  a  V-shaped  slit.  The  two  halves  after 
partially  encircling  the  larynx  do  not  meet  behind,  as  the 
signet  of  the  cricoid  cartilage  separates  them.  This  is  the 
largest  of  the  cartilages  and  is  the  one  we  have  in  mind 
when  we  speak  of  the  "Adam's  apple."  The  V-shaped  slit 
in  this  Adam's  apple  is  readily  felt  with  the  finger.  The 
sides  of  the  thyroid  cartilage  where  they  join  the  signet  of 
the  cricoid  behind  are  prolonged  upwards  into  two  horns, 
indicated  by  C  s,  in  Fig.  93.  Similar  horns,  although  not 


THE    LARYNX    AND    ARTICULATE    SPEECH.  241 

quite  so  large,  extend  downward  a  short  distance,  shown  at 
C  z,  in  the  same  figure.    On  the  signet  of  the  cricoid  behind 


Fig.  93.— THE  CARTILAGES  OF  THE  LARYNX  FROM  BEHIND. 

t,  thyroid;  Cs,  Ci,  superior  and  inferior  horns  of  thyroid;  **,  cricoid  cartilage;  t, 
arytenoid  cartilage;  Pv,  corner  to  which  the  posterior  end  of  vocal  cord  is  attached;  Pm, 
point  of  insertion  of  the  muscles  which  approximate  or  separate  the  vocal  cords;  co, 
cartilage  of  Santorini. 

are  placed  the  two  arytenoid  cartilages.  These  arytenoid 
cartilages  are  so  placed  on  the  cricoid  as  to  permit  a  good 
deal  of  motion.  They  can  be  pulled  apart,  approximated, 
and  even  rotated  by  muscles  which  reach  them.  Bach  ary- 
tenoid cartilage  is  a  triangular  structure  with  its  base  rest- 
ing on  the  cricoid.  On  the  top  of  each  arytenoid  cartilage 
is  situated  a  small  cartilage  known  as  the  cartilage  of  San- 
torini. A  little  forward  of  this  on  each  side  is  finally  a  still 
smaller  cartilage  known  as  the  cartilage  of  Wrisberg.  In 
order  to  understand  the  manipulation  of  the  voice-box,  how- 
ever, no  special  attention  need  be  paid  to  either  the  car- 
tilages of  Santorini  or  Wrisberg. 

From  the  inner  corner  of  the  base  of  each  arytenoid  car- 
tilage, marked  P  v  in  the  diagram,  there  extends  forward 
across  the  larynx  to  be  inserted  in  front  in  the  thyroid  car- 
tilage, an  elastic  membrane,  the  true  vocal  cord.  These 
cords  are,  however,  not  separate  and  distinct  strings  but 


242  STUDIES    IN    ADVANCED    PHYSIOLOGY . 

the  mucous  membrane  lining  the  larynx  is  reflected  over 
these  and  so  makes  the  vocal  cords  really  membranes,  free 
only  along  their  inner  edge.  The  analogy  of  these  mem- 
branes might  be  found  in  a  drum,  the  membrane  of  which 
had  been  slit  from  one  end  to  the  other  through  its  middle. 
As  the  forward  ends  of  the  vocal  cords  are  inserted  in  the 
immovable  thyroid  cartilage,  their  length  and  tension  must 
be  varied  by  the  movements  of  the  arytenoid  cartilages  be- 


Fig.  94.— THE  INSIDE  OF  THE  VOICE-BOX, 

a,  of  arytenoid  cartilage;  cv,  vocal  cord;  t,  thyroid  cartilage;  s,  cartilage  of  Santorini; 
cap,  articulation  of  arytenoid  with  the  cricoid  cartilage ;  c,  c,  cricoid  cartilage ;  cth,  space 
between  thyroid  and  cricoid  cartilages. 

hind.  It  was  pointed  out  that  these  cartilages  connect  with 
the  signet  of  the  cricoid  in  a  very  movable  joint,  and  there 
now  remains  the  description  of  the  muscles  by  which  the 
desired  movements  are  to  be  brought  about. 

THE  MANIPULATION  OF  THE  LARYNX. 

1. — The  movements  which  bring  the  vocal  cords  into  the 
position  found  in  quiet  breathing.  In  quiet  breathing, 
when  the  passage  of  air  through  the  larynx  produces  no  vi- 
brations, the  vocal  cords  are  relaxed  and  separated,  and  so 


THE    LARYNX    AND    ARTICULATE    SPEECH.  243 

the  slit  between  them,  called  the  glottis,  is  wide  open. 
This  widening  of  the  glottis  is  produced  by  two  sets  of  mus- 
cles called  the  crico-arytenoids  (posterior  and  anterior) . 
(The  student  will  find  much  help  in  remembering  the  names 
of  these  muscles  if  he  keeps  in  mind  that  the  name  in  every 
case  is  derived  from  the  two  cartilages  between  which  the 
muscle  exerts  its  pull.)  The  crico-arytenoid  muscles  are 
muscles  which  are  fastened  at  the  outer  basal  corner  of  the 
arytenoid,  at  the  point  marked  P  m  in  the  diagram.  From 
this  point  one  runs  forward  to  be  inserted  on  the  inner  side 
of  the  cricoid,  the  anterior  cricoid-arytenoid ;  one  backward 
to  be  inserted  on  the  back  side  of  the  cricoid,  the  posterior 
crico-arytenoid.  A  moment's  reflection  will  show  that  the 
simultaneous  contraction  of  these  two  muscles  will  tend  to 
pull  the  arytenoid  cartilage  to  which  they  are  attached  out- 
wards, and  as  this  is  true  for  both  arytenoids,  they  will  be 
pulled  apart,  and  as  the  vocal  cords  are  attached  to  these 
they  will  also  be  separated  and  the  glottis  opened.  To  make 
this  perfectly  clear  imagine  a  muscle  attached  at  the  point 
P  m ,  and  inserted  immediately  below  that  at  the  base  of  the 
cricoid.  When  that  muscle  contracts  it  is  evident  that  the 
arytenoid  will  be  pulled  out;  that  is,  away  from  its  fellow, 
and  so  the  glottis  opened. 

2. — The  movements  which  bring  the  vocal  cords  into  a 
position  to  vibrate.  In  the  production  of  vocal  sounds  the 
glottis  is  very  much  narrowed.  The  vocal  cords,  and  con- 
sequently the  arytenoids  to  which  they  are  attached,  are 
moved  towards  each  other.  This  approximation  of  the  ary- 
tenoids is  brought  about  by  two  sets  of  muscles  called 
transverse  and  oblique  arytenoids.  The  transverse  aryten- 
oids are  bands  of  muscles  which  run  from  one  arytenoid  di- 
rectly across  to  the  other.  The  oblique  arytenoids  run  from 
the  lower  portion  of  one  arytenoid  to  the  upper  portion  of 
the  second  arytenoid.  It  is  quite  obvious  that  by  the  con- 
traction of  these  two  sets  of  muscles,  transverse  and  oblique, 
the  arytenoids  will  be  pulled  together,  the  vocal  cords  at- 
tached to  them  brought  closer  together  and  the  glottis  nar- 


244  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

rowed.  When,  now,  the  air  is  driven  past  these  stretched 
membranous  flaps  they  are  set  in  vibration  and  the  tone 
arises. 

3. — Movements  which  bring  aboitt  the  change  of  the 
pitch.  Any  one  familiar  with  musical  instruments  is  aware 
that  there  are  two  ways  in  which  to  heighten  the  pitch  of  a 
string,  or  in  this  case  a  membrane.  One  method  is  to  in- 
crease its  tension,  as  we  do  by  tightening  a  violin  string, 
the  other  by  shortening  the  string,  a  procedure  also  used  on 
the  violin,  where,  by  the  placing  of  the  finger,  the  length  of 
the  string  is  varied  to  suit  the  pitch.  Both  of  these  methods 
are  used  in  the  larynx. 

First,  the  vocal  cords  are  stretched.  This  is  accom- 
plished by  the  contraction  of  muscles  which  lie  towards  the 
front  of  the  larynx,  extending  from  the  cricoid  band  to  the 
thyroid  cartilage  above  it.  This  is  the  crico-thyroid  mus- 
cle, one  of  which  lies  on  each  side  of  the  larynx.  When 
these  muscles  contract  they  pull  the  thyroid  cartilage  down 
toward  the  cricoid.  The  cricoid  band  being  fastened  se- 
curely to  the  upper  portion  of  the  trachea,  is  immovable,  and 
so  the  only  motion  possible  is  the  downward  one  of  the  thy- 
roid above  it.  But  as  the  vocal  cords  are  attached  in  front 
to  the  thyroid  cartilage  they  will  be  pulled  down  with  it  and 


.A     w 

t 

1 

1 

txEI 

1.0--^    /  2£ 

'>-->OW,j 

°  1        ^ 

d  \ 

Fig.    95. — TO     SHOW     THE     MANNER    OF    PRODUCING    CHANGES    IN    THE    PITCH  OF  HUMAN 

VOICE.     (Martin). 

For  the  explanation  of  figures  see  text. 

will  therefore  be  stretched.      Reference  to  Figure  95  will 
make  this  clear.     Here  c  is  the  signet  of  the  cricoid  carti- 


THE    LARYNX    AND   ARTICULATE    SPEECH.  245 

lage,  d  the  band  encircling  the  upper  end  of  the  trachea,  / 
and  t  parts  of  the  thyroid  cartilage,  a  the  arytenoid  carti- 
lage, v  c  the  vocal  cords.  Now,  the  crico-thyroid  muscles 
are  attached  atdfand  inserted  near  /,  and  when  they  contract 
they  pull  I  down  into  the  position  of  /'.  But  this  stretches 
the  vocal  cords,  as  the  distance  from  a  to  t  is  shorter  than 
the  distance  from  a  to  £ '.  An  apparent  paradox  appears 
here.  In  the  position  f  the  vocal  cords  are  actually 
longer  than  in  the  position  /,  and  yet  in  the  longer  position 
are  used  to  produce  higher  pitches.  Other  things  being 
equal,  the  longer  string  will  produce  a  lower  note,  but  the 
slight  increase  in  length  here  is  much  more  than  compen- 
sated by  an  increase  in  the  tension  of  it,  and  so  the  pitch 
is  raised.  It  is  this  crico-thyroid  muscle  which  is  most 
commonly  brought  into  play  in  the  change  of  the  pitch  of 
the  voice.  To  bring  the  vocal  cords,  or  rather  to  bring 
the  thyroid  cartilage  back  into  its  natural  position,  there  is 
a  muscle  lying  within  each  vocal  cord  and  extending  from 
its  insertion  in  the  arytenoid  to  its  insertion  in  the  thyroid. 
This  muscle,  the  thyro-arytenoid  is,  therefore,  the  direct 
antagonist  of  the  crico-thyroid. 

Second,  the  pitch  of  the  voice  is  also  changed  by  short- 
ening the  vocal  cords.  This  is  accomplished  by  the  crico- 
arytenoid  muscles  already  referred  to  in  explaining  the 
widening  of  the  glottis.  When  the  anterior  crico-arytenoids 
contract  it  is  evident  that  the  arytenoids  will  be  made  to 
rotate  on  their  vertical  axes  in  such  a  way  that  the  point  P  m 
is  drawn  inward  and  forward,  but  the  point  Pv  to  which  the 
vocal  cords  are  attached  drawn  outwards  and  backwards.  A 
simultaneous  contraction  of  the  two  anterior  crico-arytenoids 
would  result  in  moving  the  inner  points  (Pv)  together,  and 
if  the  contraction  were  strong  enough,  might  put  them  in 
contact.  As  the  vocal  cords  are  attached  at  the  inner 
points  they  will  be  brought  into  contact  with  each  other  and 
so  those  portions  of  the  vocal  cords  be  prevented  from  vi- 
brating. In  other  words,  the  vibrating  portion  of  each 
vocal  cord  is  made  shorter,  and  consequently  the  pitch  is 


246  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

increased.  If,  for  instance,  the  posterior  halves  of  the  vocal 
cords  were  touching  and  so  not  sounding,  the  sounding 
portion  would  be  only  half  as  long  as  before,  and  our  knowl- 
edge of  music  would  make  it  evident  that  the  pitch  would 
be  just  an  octave  higher.  For  when  a  violin  string  is 
pressed  down  at  this  middle  point  its  pitch  is  raised  by  one 
octave.  By  varying  the  length  along  which  the  vocal 
cords  are  thus  pressed  against  each  other,  that  is,  by  vary- 
ing the  length  of  the  sounding  vocal  cord,  a  corresponding 
range  in  pitch  is  effected. 

4. — The  range  of  the  humaji  voice.  The  range  of  the 
human  voice  is  not  far  from  three  octaves,  although  great 
singers  have  frequently  exceeded  this.  On  account  of  the 
much  shorter  voice-box  in  children,  the  pitch  of  their 
voices  is  much  higher.  In  the  case  of  boys  there  occurs  about 
the  time  of  puberty  a  somewhat  rapid  elongation  of  the 
vocal  cords,  referred  to  in  the  common  expression,  the 
"breaking  of  the  voice. ' '  This  elongation  causes  a  material 
deepening  of  the  voice,  but  as  the  elongation  is  not  the 
same  for  all  individuals,  so  there  are  differences  in  pitch 
which  we  recognize  in  designating  some  as  bass  singers, 
others  as  tenor  singers.  In  the  case  of  girls  no  such  elong- 
ation of  the  vocal  cords  seems  to  take  place,  and  so  the 
pitch  of  a  woman's  voice  remains  about  an  octave  higher 


-Sopran — 


-Alt- 


FGABcdefga'bcd  e  f  g  a  bed  e  f  g  a   1}  c 
Bass 


-Tenor- 


Fig.  96.— THE  ORDINARY  RANGE  OF  VOICE. 


through  life.  The  average  range  of  the  human  voice  for 
the  four  usual  divisions,  bass,  tenor,  alto  and  soprano,  is 
indicated  in  the  accompanying  diagram. 


THE   LARYNX    AND   ARTICULATE   SPEECH.  247 

SPEECH. 

Speech  is  a  combination  of  vocal  sounds  (vowels) ,  with 
noises  (consonants) .  Vowels  have  musical  and  harmonic 
properties ;  consonants  are  not  tones  in  this  sense  at  all . 

The  vowels,  A,  K,  I,  O,  U,  and  their  derivatives  are 
produced  by  changing  the  relative  dimensions  of  the  reson- 
ance cavities  connected  with  the  voice-box.  As  far  as  the 
vocal  cords  are  concerned  the  same  vibrations  might  pro- 
duce all  of  the  different  vowels.  Which  vowel  it  shall  be  is 
determined  by  the  resonance  cavities .  Thus ,  no  matter  which 
vowel  we  sound,  the  vocal  cords  act  alike  if  the  pitch  be 
the  same,  and  whether  it  shall  be  A,  E,  I,  O,  U,  or  any  of 
their  derivatives  will  depend  upon  the  quality  or  timbre 
which  is  given  to  these  vibrations  by  the  sounding  cavities. 
Any  one  can  assure  himself  of  this  by  sounding  A,  as  in 
father,  and  then  without  any  change  in  the  vocal  cords 
change  his  mouth  to  the  position  of  O,  and  then  OO.  I  is, 
of  course,  a  combination  consisting  of  A,  as  in  father,  and 
E  as  in  feet.  The  same  is  true  of  U,  consisting  of  E,  as  in 
feet,  and  OO  as  in  loose.  That  the  production  of  the 
vowels  is  dependent  upon  the  form  of  the  resonance  cavities 
is  a  subject  which  each  person  interested  can  so  easily 
verify  for  himself  that  further  discussion  seems  unnecessary. 

Consonants  are  sounds  which  are  produced  in  most  in- 
stances with  little  help  of  the  vocal  cords,  but  are  brought 
about  by  modifications  of  the  manner  in  which  the  blast  of 
air  is  expelled  through  the  mouth.  For  instance,  the  cur- 
rent of  air  may  be  interrupted  near  the  teeth,  as  in  the  con- 
sonant T,  or  by  the  tip  of  the  tongue,  as  in  the  letter  D,  or 
by  the  lips,  as  in  the  letter  P,  or  even  by  the  soft  palate  at 
the  root  of  the  tongue,  as  in  the  letter  G  (in  the  word  go) . 
Some  of  the  consonants  are  produced  by  a  sudden  explosive 
blast  of  airj  as  for  instance.  D,  G,  B,  K,  T,  P.  Others  are 
continuous,  being  produced  by  the  rush  of  air  through  nar- 
row passages  either  between  the  lips,  as  in  F,  or  the  teeth, 
as  in  S,  or  when  the  approximation  is  still  closer,  as  in  TH. 
In  the  case  of  L,  the  tongue  is  pressed  against  the  hard 


248  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

palate  and  the  air  allowed  to  escape  on  its  sides.  With 
some  consonants  there  is  an  admixture  of  vocal  sounds,  as 
in  B,  D,  G  (hard),  V  and  Z.  In  the  production  of  other 
consonants  the  nose  is  called  into  play  as  a  resonance  cav- 
ity, and  so  arise  M,  N  and  NG.  In  the  consonant  R  there 
is  a  vibratory  motion,  either  dental,  as  is  more  common  in 
the  English  language,  or  gutteral,  more  usual  in  the  Ger- 
man. H,  finally,  is  hardly  more  than  a  laryngeal  sound, 
little  more  than  hard  breathing. 

Whispering  differs  from  true  speech  in  the  absence  of 
all  vowels.  It  is,  therefore,  in  a  physical  sense,  a  noise 
only.  In  whispering,  although  the  glottis  is  considerably 
narrowed,  the  cords  are  not  stretched  enough  to  vibrate, 
and  the  air  made  to  rush  past  them  is  therefore  thrown,  not 
into  regular,  but  into  irregular  vibrations .  Such  irregular  vi- 
brations as  happen  to  coincide  in  period  with  the  air  in  the 
throat  or  mouth  serve  to  characterize  the  vowels,  while  con- 
sonants are  produced  in  the  ordinary  way. 

In  the  discussion  of  the  voice  reference  has  always  been 
to  what  is  commonly  known  as  the  chest  voice.  It  is  pos- 
sible in  addition  to  produce  what  are  called  falsetto  tones, 
but  the  manner  in  which  this  is  accomplished  is  not  yet 
satisfactorily  known. 


CHAPTER  XL 

GLANDS    AND    THE    GENERAL    PHYSIOLOGY   OF 
SECRETION. 

HISTORICAL. 

The  ancients  had  practically  no  knowledge  of  secretion. 
They  thought  that  the  phlegm  from  the  nose  was  a  dis- 
charge from  the  brain.  Their  other  views  were  not  less 
mistaken.  This  misconception  lasted  until  1660,  when 
Schneider's  researches  on  the  olfactory  membrane  proved 
its  falsity.  About  this  time,  too,  a  number  of  eminent  an- 
atomists appeared,  whose  researches  on  the  structure  of 
glands  materially  cleared  up  the  meaning  of  these  organs. 
The  names  of  many  of  these  noted  anatomists  are  still  re- 
tained in  connection  with  the  terminology  of  glands.  Thus, 
Glisson  (Capsule  of  Glisson  in  the  liver),  Stenson  (Duct  of 
Stenson  in  the  salivary  glands),  Peyer  (Patches  of  Peyer  in 
the  intestines),  Brunner  (Glands  of  Brunner  in  the  duode- 
num), and  Malpighi  (Malpighian  corpuscles  of  kidneyj. 
Our  anatomical  knowledge  became  finally  fairly  complete 
when  in  1830  Johann  Mueller's  large  treatise  on  glands  was 
published. 

Thus  far,  all  the  work  had  been  of  an  anatomical  nature 
and  the  physiological  process  of  secretion  remained  for 
some  time  longer  entirely  unknown.  The  view  held  was 
that  the  blood  capillaries  actually  communicated  with  the 
ultimate  tubules  of  the  ducts  of  the  gland,  and  that  the 
secretion  was  a  kind  of  direct  separation  from  the  blood,  in 
which  the  corpuscles  did  not  take  part,  because  the  smaller 
tubules  of  the  duct  were  too  tiny  to  allow  them  to  pass  from 
the  blood.  The  correct  view  of  the  process  of  secretion, 
however,  soon  followed  the  discovery  of  the  cellular  struc- 
ture of  animal  tissues  by  Schwann,  and  the  discovery  of 

(249) 


250  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

the  physical  process  of  osmosis.  The  influence  of  the 
nerves  on  secretion  was  then  demonstrated  in  vivisections 
made  by  Ludwig  in  1851,  who  by  electrically  stimulating 
the  cerebral  nerve  going  to  the  submaxillary  of  the  dog 
caused  a  secretion  of  saliva,  which  rose  to  the  height  in  the 
tube  of  200  millimeters  of  mercury,  while  the  height  of  the 
blood  in  the  carotid  artery  rose  to  112  millimeters  of  mer- 
cury only.  The  action  of  the  sympathetic  nerve  on  secretion 
and  the  changes  of  the  vascular  supply  of  glands  were  in 
1858  discovered  by  Claude  Bernard.  Finally  the  micro- 
scopist,  Heidenhain,  made  a  series  of  researches  on  the 
histological  changes  in  secreting  cells,  which  have  demon- 
strated that  the  secreting  cells  themselves  are  the  seat  of 
active  chemical  changes  which  form  the  secretions. 

SECEETION. 

The  term  "secretion"  is  frequently  made  to  apply  to  a 
varying  number  of  things.  Sometimes  all  the  substances 
which  are  given  off  by  the  blood  are  called  secretions.  This 
would  make  the  lymph  which  oozes  out  of  blood  capillaries 
a  secretion,  and  would  also  make  the  gases  which  figure  in 
respiration  secretory  products.  This  use  of  the  term  secre- 
tion is,  however,  much  too  wide,  for  physiologically  speak- 
ing, lymph  and  the  blood  gases  do  not  figure  in  any  way  as 
the  product  of  glands  proper.  In  the  second  place,  the 
term  "secretion"  is  made  to  apply  to  all  the  discharges  of 
all  the  various  glands.  There  is  no  special  objection  to  this 
application  of  the  term.  Other  physiologists,  however,  speak 
of  secretions  and  excretions,  calling  "secretions"  those 
products  of  the  glands  which  are  intended  for  a  further  use 
in  the  body,  and  apply  the  term  "excretions"  to.  those 
glandular  discharges  which  are  intended  for  no  further  use, 
but  are  simply  to  be  thrown  off.  But  even  these  uses  of 
the  term  are  not  satisfactory,  because  it  is  not  always  easy 
to  tell  whether  a  certain  secretion  is  directly  intended  for 
further  use,  or  is  a  mere  waste  product  to  be  eliminated. 
To  do  away  with  such  an  ambiguity,  therefore,  the  term 


GLANDS,  GENERAL  PHYSIOLOGY  OF  SECRETION.   251 

secretion  is  here  applied  to  all  the  products  of  all  the 
glands.  Before  following  out  in  detail,  now,  what  the  ex- 
act process  of  secretion  is,  it  is  necessary  to  turn  to  the 
anatomy  of  glands. 

1. — Glands  and  Their  Anatomy.  Here  additional  am- 
biguities are  at  once  misleading.  There  are  a  number  of 
structures  in  the  body  designated  as  glands  which  are  not 
true  glands  in  any  sense  of  that  term.  They  were  called 
glands  by  anatomists  who  were  ignorant  of  their  real 
nature,  and  these  names  given  to  them  in  this  way  still 
cling  to  them  in  spite  of  our  knowledge  that  they  are  not 
glands  at  all.  Just  as  we  call  the  primitive  inhabitants  of 
America  Indians  without  intending  to  express  in  any  way 
the  misconception  that  they  are  residents  of  the  East 
Indies.  Such  entirely  different  structures  are  the  pineal 
gland  of  the  brain,  which  instead  of  being  a  gland  is 
really  but  the  stump  of  an  optic  nerve.  Such  structures, 
too,  are  the  lymphatic  glands,  which  are  aggregations  of 
white  blood  corpuscles,  and  have  absolutely  nothing  to  do 
with  secretion  in  any  way. 

In  addition  to  the  structures  just  mentioned,  which  are 
at  the  very  first  glance  seen  to  belong  to  entirely  different 
tissues,  we  have  several  structures  which,  while  they  may 
be  the  seat  of  chemical  changes  in  the  blood  passing  through 
them,  yet  have  no  ducts,  and  do  not  pour  out  distinct  secre- 
tions. They  are,  therefore,  not  infrequently  called  "duct- 
less" glands.  Examples  of  such  are  the  spleen,  the  thyroid 
gland  and  the  adrenal  glands.  Disregarding  all  these,  then, 
it  may  be  said  that  a  typical  gland  consists  of  a  basement 
membrane  of  connective  tissue  bearing  a  surface  of  secret- 
ing cells  on  one  side,  and  supplied  with  numerous  blood 
vessels  on  the  other.  In  addition  to  these  three  main  ele- 
ments there  are,  of  course,  nerves  which  in  some  instances 
have  actually  been  traced  by  anatomists  into  the  secreting 
cells  themselves.  Finally  in  the  interstices,  as  in  all  other 
tissues,  are  the  lymphatics.  It  will  be  seen  from  this  that 


252 


STUDIES   IN   ADVANCED    PHYSIOLOGY. 


a  gland  is  but  a  surface  of  secreting  cells  supported  by  a  base- 
ment membrane,  richly  supplied  with  blood-vessels  under- 
neath the  membrane,  and  subject  to  the  control  of  nerves. 


Fig.  97.— FORMS  OF  GLANDS.    SIMPLE  SACCULAR  GLAND  FROM  AMPHIBIAN  SKIN.    (Flem- 
ming.)    SIMPLE  TUBULAR  GLAND  FROM  HUMAN  INTESTINE.     (Flemming.)    GLAND 

FORMED  OF  A  SIMPLE  DUCT-SYSTEM.     (Flemming.)     CONSTRUCTION  OF  A   LOBULE  OF 

A  COMPOUND  RACEMOSE  GLAND  (a,  duct;  &,  6,  branches  of  duct;  c,  secreting  alveoli). 
PART  OF  A  SMALL  RACEMOSE  GLAND,  SHOWING  THE  TUBULAR  CHARACTER  OF  THE 
ALVEOLI.  (Flemming.) 

A  gland,  however,  spread  out  as  such  a  flat  surface, 
would  take  up  a  very  great  deal  of  room  in  order  to  secrete 
the  amounts  necessary  to  the  body.  To  save  space,  there- 
fore, these  glandular  surfaces  become  pitted  in  and  folded, 
and  in  this  manner  result  the  various  forms  of  glands.  Ex- 
amples of  the  typical  surface  glands  are  not  wanting.  Thus, 
the  peritoneum,  the  pleura  and  the  pericardium  have  such 


GLANDS,    GENERAL  PHYSIOLOGY  OF   SECRETION.       253 

flat  surfaces  which  secrete  the  serous  fluids.  Nearly  all  the 
other  glands,  however,  are  modified.  Usually  space  is  saved 
by  pitting  in  the  secreting  surface  and  thus  tubular  glands 
arise.  Sometimes  these,  instead  of  being  straight  and 
tubular,  become  rounded  and  sac-like,  in  which  case  such 
a  gland  is  called  a  racemose  gland.  When  several  such 
tubular  or  racemose  glands  have  a  common  duct  leading 
from  them,  the  entire  structure  is  spoken  of  as  a  compound 
gland.  . 

Illustrations  of  the  simple  tubular  glands  may  be  found 
in  the  gastric  glands  of  the  stomach,  and  in  the  crypts  of 
Ljeberkiihn.  Illustrations  of  the  simple  racemose  glands 
occur  in  the  sebaceous  or  oily  glands  of  the  skin.  How- 
ever, most  of  the  larger  glands,  such  as  the  pancreas  and 
the  salivary  glands,  are  of  the  compound  racemose  kind. 
Such  a  compound  racemose  gland  might  be  compared  to  a 


Fig.  98.— SECTION  OF  A  RACEMOSE  GLAND,  SHOWING  THE  COMMENCEMENT  OF  A  DUCT 

IN   THE   SECRETING  ALVEOLI.      (After  Shafet.) 

a,  an  alveolus;    6,  basement  membrane  lining  the  duct  d';  c,  connective  tissue  be- 
tween the  alveoli;  d,  duct;  s,  semilunar  reserve  cells. 

very  full  bunch  of  grapes  in  which  the  central  stalk  figures 
as  the  single  duct,  while  the  individual  grapes  represent  the 
ultimate  sac-like  expansions,  in  which  the  process  of  secre- 


254  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

tion  occurs.  If,  now,  between  such  bunches  of  grapes  we 
should  imagine  a  very  full  network  of  blood-vessels  and  a 
supply  of  nerves,  we  should  have  a  coarse  but  possibly  a 
helpful  analogy. 

2. — The  Process  of  Secretion.  Such  an  arrangement  of 
a  gland  with  a  basement  membrane  and  blood-vessels  natur- 
ally suggests  the  possibility  of  secretion  being  a  mere  case 
of  physical  filtration.  We  know,  for  instance,  that  if  a 
liquid  containing  things  in  solution  be  put  into  a  membran- 
ous bag,  such  a  liquid  by  the  process  of  osmosis  reaches 
the  outside.  There  are,  however,  certain  facts  which  make 
it  at  once  perfectly  plain  that  the  process  of  secretion  is  not 
a  process  of  physical  filtration.  Quite  a  number  of  glands 
secrete  substances  which  are  not  found  in  the  blood  at  all. 
They  secrete  substances  which  they  themselves  have  pro- 
duced. Thus,  for  instance,  the  pepsin  of  the  stomach,  or 
trypsin  of  the  pancreas,  and  the  ptyalin  of  the  salivary 
glands  are  not  contained  in  blood  at  all.  Such  special  pro- 
ducts which  the  glands  have  themselves  produced  are  called 
specific  elements.  In  this  sense  we  speak  of  the  hydro- 
chloric acid,  rennet,  and  pepsin  of  the  stomach  as  the  spe- 
cific elements  of  that  organ.  If  secretion  were  a  physical 
filtration,  specific  elements  would  be  impossible. 

But  the  question  then  recurs,  may  not  the  remaining 
elements  of  a  secretion  be  merely  filtered  through.  This 
question  must  be  answered  in  the  negative  for  several  rea- 
sons. First,  glands  secrete  at  certain  times  only,  while  if  it 
were  a  physical  filtration  the  process  ought  to  go  on  all  the 
time,  for  even  when  a  gland  is  at  rest  the  blood  circulates 
through  it  freely.  Second,  a  certain  poison  called  atropine 
(of  frequent  use  in  the  physiological  laboratory)  destroys 
the  secreting  power  of  a  gland  at  once,  but  it  does  not 
change  the  blood  pressure  in  the  gland  at  all.  Such  a 
poisoning  action  would  be  impossible  in  the  case  of  simple 
filtering.  Third,  glands  may  be  stimulated  to  such  increased 
action  that  the  pressure  of  the  secretion  may  actually  ex- 
ceed the  pressure  of  the  blood  in  the  gland;  a  condition  of 


GLANDS,  GENERAL  PHYSIOLOGY  OF  SECRETION.   255 

things  never  possible  in  simple  osmosis.  Fourth,  glands 
may  be  made  to  secrete  even  when  they  contain  no  circu- 
lating blood.  Thus,  if  the  sciatic  nerve  in  an  amputated 
limb  of  an  animal  be  stimulated  the  sweat  glands  may  be 
made  to  secrete,  when  it  is  evident  that  there  is  no  circu- 
lating blood  in  the  severed  limb.  We  are  driven,  therefore, 
to  the  conclusion  that  secretion  is  a  phenomenon  of  the  liv- 
ing gland  cells  themselves,  and  its  ultimate  nature  we  un- 
derstand as  little  as  we  do  the  ultimate  nature  of  muscle 
activity  or  nervous  impulses.  It  is  a  chemical  process  whose 
explanation  is  not  yet  at  hand. 

3. — Histological  Changes  in  Secreting  Cells.  On  the 
other  hand,  while  we  do  not  understand  the  exact  nature  of 
the  process  of  secretion,  we  are  able  to  observe  on  a  gland 
certain  histological  changes  in  rest  and  in  action.  Thus, 
when  a  gland  starts  to  secrete  it  at  once  becomes  flushed 
with  blood,  due  to  the  enlargement  of  the  arteries  traversing 
it.  Such  a  dilatation  has,  however,  nothing  to  do  with  the 
gland  itself,  but  has  been  brought  about  by  nerves  which  run 
to  the  arteries  direct,  and  which  were  stimulated  at  the 
same  time  the  gland  cells  were  stimulated.  The  purpose  of 
such  an  increase  in  the  supply  of  blood  to  a  working  gland 
is,  of  course,  very  apparent.  It  is  to  carry  abundant  ma- 
terial to  the  gland,  and  supply  it  with  sufficient  amounts  of 
oxygen  to  sustain  its  activities.  It  differs  in  no  essential 
way  from  the  condition  of  things  in  a  working  muscle. 

But  histological  changes  may  be  observed  in  the  secret- 
ing cells  themselves,  for  a  gland  that  has  been  actively 
secreting  looks  quite  different  under  the  microscope  from 
one  which  has  been  at  rest  for  some  time.  If,  for  instance, 
two  animals  as  nearly  alike  as  possible  be  taken,  and  one 
of  them  be  starved  for  a  day,  and  thus  the  pancreas  of  that 
animal  be  given  no  occasion  to  pour  out  its  secretion,  and 
the  animal  be  then  killed  and  the  pancreas  observed  histo- 
logically,  it  may  be  seen  that  the  gland  cells  are  distended 
and  that  their  outer  portions,  that  is,  the  portions  next  to 
the  lumen  of  the  gland,  are  filled  with  granules,  while  those 


256 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


portions  of  the  cells  next  to  the  basement  membrane  seem 
clearer  and  more  protoplasmic.  If,  now,  for  comparison 
with  this  gland  there  be  examined  the  pancreas  of  the  sec- 
ond animal,  which  was  plentifully  fed  eight  or  ten  hours 
before  being  killed,  quite  a  different  appearance  of  the 
secreting  cells  is  at  once  evident.  The  cells  seem  smaller, 
and  the  granular  layer  is  almost  wholly  absent,  the  whole 
cell  now  from  basement  membrane  to,  lumen  appearing 
clear. 

It  is  not  difficult  to  account  for  the  relative  appearances 
of  these  two  glands.  In  the  working  gland  which  has  just 
been  called  upon  for  a  copious  secretion  the  granules  have 
been  used  up;  have,  in  other  words,  been  changed  into  a 
part  of  the  secretion  of  the  gland.  If,  however,  a  gland 
which  has  been  copiously  secreting,  be  given  opportunity 
to  recuperate,  the  granules  again  begin  to  appear,  become 


Fig.  99.— PARTS  OF  GLANDS.    (After  I^angley.) 

A,  at  rest,  almost  filled  with  zymogen  granules;  B,  after  a  short  period  of  activity; 
C,  after  a  prolonged  secretion.    In  A  and  B,  the  nuclei  are  obscured  by  the  granules. 

more  and  more  plentiful,  and  soon  occupy  almost  half  of 
the  space  of  the  cell.  The  condition  of  things  is  then  this: 
In  the  process  of  secretion  the  pancreatic  cells  (which 
gland  is  here  used  as  an  illustration  of  glands  in  general) 
change  these  stored-up  granules  into  the  secretion,  while 
during  the  period  of  apparent  rest  the  gland  seems  engaged 
in  manufacturing  and  storing  up  these  granules  ready  for 
the  next  secretion.  It  will  thus  be  seen  that  the  process  of 
secretion  in  cells  is  essentially  a  process  of  growth.  The 
secreting  cells  take  proper  nourishment  from  the  blood 
bathing  them,  and  in  that  way  construct  within  themselves, 


GLANDS,  GENERAL  PHYSIOLOGY  OF  SECRETION.   257 

possibly  out  of  their  own  substance,  the  specific  elements 
in  question.  Somewhat  like  a  sheep  by  taking  the  proper 
nourishment  into  its  body,  and  by  chemical  changes  in  its 
tissues,  may  produce  the  woolly  covering  of  the  skin. 

That  the  specific  elements  of  glands  are  thus  built  out 
of  the  cells  themselves  is  especially  well  shown  in  the  case 
of  the  oil  glands  of  the  skin.  In  those  glands  some  of  the 
cells  may  be  seen  to  grow  large,  then  by  internal  chemical 
changes  their  own  substance  apparently  disintegrates  into 
oil,  a  change  which  continues  until  finally  the  whole  cell 
falls  into  pieces,  and  its  debris  forms  the  secretion.  In 
other  cells  the  destruction  is  not  complete,  but  only  por- 
tions of  the  cell  break  up  into  the  secretion  in  question.  In 
such  cases,  of  course,  an  individual  cell  by  continuing  to 
grow  and  continuing  to  form  out  of  its  substance  the  spe- 
cific element  may  remain  active  for  an  indefinite  time,  while 
in  the  case  of  cells  where  the  disintegration  is  complete, 
new  cells  must  continually  be  forming  to  replace  those  that 
break  down. 

In  the  case  of  the  pancreas  a  complete  destruction  of 
the  cells  does  not  occur,  as  it  does  in  the  case  of  the  oil 
gland.  To  take  a  not  very  close  analogy, the  secretion  of  a 
gland  is  not  a  product  made  by  the  cell  in  the  same  sense 
that  a  table  is  a  product  made  by  a  carpenter,  but  the  secre- 
tion is  a  product  derived  from  the  cell  substance  itself,  as 
the  table  is  a  product  of  the  oak  tree. 

In  the  case  of  the  pancreas  these  granules  are  not,  how- 
ever, identical  with  its  specific  element.  The  main  specific 
element  of  the  pancreas  is  called  trypsin,  whose  marked 
influence  in  digestion  will  be  discussed  later.  But  the 
granules  in  the  pancreas  cells  are  not  trypsin.  They  are 
some  antecedent  substance  out  of  which,  however,  by  slight 
changes  trypsin  is  produced.  The  granules  are  called  tryp- 
sinogen  granules;  that  is,  by  the  etymology  of  that  word, 
the  producers  of  trypsin. 

Several-  fortunate  circumstances  arise  by  this  arrange- 
ment. Trypsin  is  soluble  and  could  not  easily  be  stored  up  in 
17 


258  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  gland.  It  has  a  digestive  action  which  might  lead  it  to 
attack  the  gland  itself  in  which  it  is  stored.  Both  of  these 
difficulties  are  avoided  by  forming  the  trypsinogen  granules. 
These  are,  in  the  first  place,  solid  and  can  easily  be  stored. 
In  the  second  place  they  do  not  have  the  active  digestive 
properties  of  the  trypsin  and  so  exert  no  digestive  action  at 
all.  When,  then,  finally  the  trypsin  is  needed  all  this  stored 
trypsinogen  may  by  slight  changes  be  at  once  transformed 
into  trypsin  and  so  poured  out  in  large  quantities  into  the 
intestines.  Trypsin  is  a  digestive  fluid  of  rather  complex 
composition  and  it  would  be  practically  impossible  for  the 
pancreas  to  secrete  large  quantities  of  this  at  sudden  notice, 
but  by  devoting  all  of  its  resting  period  to  the  production 
of  these  trypsinogen  granules,  storing  these  up  in  the  outer 
part  of  each  cell,  and  then  just  at  the  moment  when  the 
trypsin  is  needed  changing  these  trypsinogen  granules  into 
the  soluble  trypsin,  sudden  and  large  quantities  of  trypsin 
are  at  once  available. 

What  has  been  said  with  reference  to  the  pancreas  applies 
to  the  mucous  glands.  Here  during  rest  are  produced  gran- 
ules which  at  the  proper  occasion  are  changed  into  mucus 
and  poured  out.  These  stored  granules  are  called  mucino- 
gen  granules.  While  it  has  been  impossible  to  actually 
demonstrate  a  similar  condition  of  things  in  the  gastric 
gland,  there  is  every  reason  to  believe  that  here,  also,  dur- 
ing the  resting  period  of  the  stomach  the  peptic  cells  are 
storing  up  granules  of  pepsinogen.  Such  granules  not  being 
easily  dialyzable  could  be  stored  in  the  cell,  and  not  having 
the  active  digestive  property  of  regular  pepsin,  would  exert 
no  chemical  effect  on  the  glands  themselves.  Then,  at  the 
moment  food  enters  the  stomach,  these  pepsinogen  granules 
are,  by  slight  additional  changes,  transformed  into  the  pep- 
sin and  so  poured  on  the  food.  Possibly  a  similar  antece- 
dent substance  is  present  in  the  salivary  glands  from  which 
the  specific  element  ptyalin  is  derived,  a  kind  of  ptyalino- 
gen.  It  is  well,  however,  to  keep  in  mind  that  the  actual 
presence  of  granules  of  the  nature  just  described  can  be 


GLANDS,  GENERAL  PHYSIOLOGY  OF  SECRETION.   259 

easily  demonstrated  in  the  case  of  the  pancreas  and  the  mu- 
cous glands  only,  and  that  its  application  to  other  glands  is 
upon  probable  grounds  only. 

THE  INNERVATION  OF  GLANDS. 

That  glands  are  under  direct  nervous  control  is  a  matter 
of  every-day  experience.  The  tear  glands  respond  at  once 
to  intense  emotions,  and  the  common  expression  to  have 
one's  "mouth  water"  shows  that  the  salivary  glands  are  di- 
rectly influenced  by  states  of  mind.  Such  nervous  influ- 
ences are  not  so  apparent  in  the  case  of  the  sweat  glands, 
but  even  there  intense  emotion  or  anxiety  may  produce  a 
copious  sweating  even  when  the  surrounding  temperature 
would  tend  the  other  way.  In  the  case  of  the  stomach 
and  pancreas  there  are  such  evidences  of  innervation.  Se- 
cretion in  the  stomach  at  once  induces  secretion  in  the  pan- 
creas, explained  only  by  the  fact  that  these  two  organs  are 
connected  by  nerves.  There  is  no  more  reason  why  glands 
should  be  automatic,  that  is,  independent  of  nervous  con- 
trol, than  why  muscles  should  be.  Glandular  activity  is  no 
less  an  activity  than  muscular  exertion.  The  regulation  of 
the  periods  of  secretion  so  that  the  product  may  be  availa- 
ble just  at  the  moment  that  it  is  needed  could  be  effected 
only  by  nervous  control.  The  saliva  flows  when  food  is 
masticated  in  the  mouth,  the  gastric  or  pancreatic  juices 
are  poured  into  the  alimentary  canal  as  soon  as  the  mucous 
membrane  in  stomach  and  intestine  is  stimulated  by  enter- 
ing foods,  while  the  gall-bladder  contracts  and  pours  its 
contents  of  bile  into  the  duodenum  for  the  same  reason. 

The  manner  of  the  innervation  of  glands  has,  however, 
been  worked  out  carefully  and  explicitly  in  the  case  of  the 
salivary  glands  only,  and  the  account  here  given  is  that  of 
the  submaxillary  gland  itself,  but  there  is  every  reason  to 
believe  that  in  the  main  the  nervous  arrangement  of  the 
other  glands  is  the  same.  In  order  to  understand  how  this 
has  been  worked  out,  a  few  experiments  in  the  stimulation 


260  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

of  the  nerves  going  to  the  submaxillary  gland  will  materi- 
ally aid: 

1. — The  cerebro-spinal  nerves.  If  the  nerve  coming 
from  the  brain  and  going  to  the  submaxillary  gland  be  cut, 
and  the  end  of  the  nerve  connected  with  the  gland  be  stim- 
ulated, a  copious  secretion  of  saliva  immediately  results.  At 
first  the  saliva  is  perfectly  normal,  but  as  the  gland  is  being 
stimulated  longer  and  longer,  the  secretion  becomes  more 
and  more  watery,  and  finally  contains  little  else  than  water 
and  dissolved  salts.  The  ptyalin,  the  specific  element  of 
saliva  and  the  mucin  are  no  longer  present.  If  the  nerve 
or  gland  be  not  too  much  affected  by  excessive  work  such  a 
secretion  of  watery  saliva  may  be  continued  for  a  long 
time. 

From  this  experiment  it  is  evident  that  the  nerve  from 
the  brain,  the  corda  tympani,  as  it  is  usually  called,  causes 
an  abundant  flow  of  a  watery  secretion  from  the  gland,  but 
does  not  seem  to  be  directly  concerned  in  the  production  of 
any  of  the  specific  elements  of  the  secretion.  What  the 
gland  pours  out  is  simply  material  which  it  has  taken  from 
the  blood.  It  is  not  anything  which  the  gland  has  made 
itself.  Such  parts  of  a  secretion  which  are  derived  directly 
from  the  blood  are  called  transudations,  and  it  seems  that 
the  cerebro-spinal  nerve  is  therefore  directly  concerned 
with  the  transudations.  These  transudations,  however, 
serve  to  wash  the  specific  elements  out  of  the  gland.  For 
this  reason  the  saliva  which  first  begins  to  flow  contains 
ptyalin  and  mucin,  because  these  elements  were  stored  up 
in  the  gland  and  were  then  washed  out.  But  as  soon  as 
this  stored  supply  is  exhausted  nothing  but  the  transuda- 
tions continue.  These  transudations  may,  then,  flow  from 
the  gland  for  an  indefinite  period,  because  as  the  blood 
supply  in  the  gland  is  kept  constant  the  source  from  which 
the  transudations  are  derived  does  not  diminish.  When, 
finally,  such  a  gland  stops  secreting  it  is  probably  more  a 
nervous  exhaustion  than  a  glandular  one.  This  will  ex- 


GLANDS,  GENERAL  PHYSIOLOGY  OF  SECRETION.   261 

plain  why  the  flow  of  tears  may  continue  indefinitely,  the 
lachrymal  secretion  being  entirely  a  transudation  and  con- 
taining no  specific  element  of  the  lachrymal  glands  them- 
selves'. It  will  also  explain  why  by  thinking  of  palatable 
foods,  etc.,  the  mouth  begins  to  water.  It  is  a  stimulation 
of  the  cerebro-spinal  nerve,  the  result  of  which  is  an  im- 
mediate flow  of  the  transudatory  part  of  the  saliva.  It  must 
not  be  imagined,  however,  that  the  flow  of  tears  or  the  flow 
of  this  watery  saliva  is  a  mere  filtration  from  the  blood.  It 
is  an  actual  picking  up  of  these  materials  from  the  blood  by 
the  gland  cells  themselves.  If  it  were  a  mere  filtration 
there  is  no  reason  why  the  tears  should  not  flow  at  an  un- 
varying rate  all  the  time. 

2. — The  sympathetic  nerves.  In  addition  to  the  cerebro- 
spinal  nerve  to  the  submaxillary  gland  this  gland  is  supplied 
with  branches  from  the  sympathetic  system.  When  these 
nerves  are  stimulated  the  gland  begins  to  secrete  saliva, 
also,  but  the  saliva  is  now  of  an  entirely  different  kind. 
Instead  of  being  watery  it  now  becomes  exceedingly  viscid 
and  ropy,  and  contains  a  much  greater  proportion  of  the 
specific  elements  of  the  secretion.  Continued  stimulation 
of  the  sympathetic  nerve  may  cause  the  saliva  to  cease 
flowing  altogether ;  but  this  is  because  the  secretion  has  be- 
come so  thick  and  concentrated  that  it  is  not  able  to  force 
its  way  through  the  delicate  tubes.  Evidently  the  sympa- 
thetic nerve  has  to  do  with  the  production  of  the  specific 
elements  themselves,  and  in  no  integral  way  whatever  is  it 
concerned  with  the  transudation  elements.  It  seems  to 
govern  the  production  of  those  things  which  the  gland  must 
make  for  itself  and  store  up.  If,  now,  after  the  sympa- 
thetic nerve  has  been  stimulated  for  some  time  and  the 
saliva  has  thus  been  made  thick  and  ropy,  the  cerebro- 
spinal  nerve  be  also  stimulated,  there  is  at  once  a  copious 
flow  of  saliva.  Under  the  influence  of  the  latter  nerve  large 
quantities  of  water  and  mineral  salts  are  actively  picked  up 
by  the  gland  from  the  blood  and  passed  through  into  the 
tubules,  washing  out  the  specific  elements  formed. 


262  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

There  is,  therefore,  no  difficulty  in  interpreting  these 
phenomena.  To  restate  it,  it  is  this.  The  gland  cells  re- 
ceive two  kinds  of  nerves.  First,  those  from  the  cerebro- 
spinal  system,  which  when  stimulated  cause  the  transuda- 
tions  to  wash  the  specific  elements  out  of  the  glands. 
Secondly,  the  sympathetic  nerves  which  control  the  pro- 
duction of  the  specific  elements  themselves.  The  sympa- 
thetic nerve  is  no  doubt  more  or  less  in  action  all  the  time, 
and  in  this  way  the  gland  is  busy  in  the  production  of  the 
specific  elements  in  the  periods  of  apparent  rest  when  there 
is  no  secretion  flowing  from  the  gland,  while  the  cerebro- 
spinal  nerve  is  called  into  play  at  the  moment  the  secretion 
is  wanted,  and  brings"  about  a  copious  flow  of  water  and 
mineral  salts  through  the  gland,  by  means  of  which  these 
specific  elements  are  carried  out.  Of  course  just  at  this 
time  the  stored  antecedent  granules  in  the  various  glands 
are  finally  changed  into  the  regular  specific  elements; 
otherwise  the  transudations  would  not  be  able  to  carry  them 
out.  For  instance,  in  the  pancreas  the  trypsinogen  granules 
would  not  be  affected  by  the  water  and  salt  secreted,  but  it 
would  at  that  point  change  into  the  soluble  trypsin  which  is 
readily  washed  out. 

It  was  pointed  out  before  that  along  with  the  stimula- 
tion of  the  cerebro-spinal  nerve  there  is  a  stimulation  of  the 
vaso-dilator  nerves  going  to  the  arteries  of  the  glands,  so 
that  while  the  transudations  are  being  poured  Out  of  the 
gland  the  gland  itself  seems  flushed  with  the  distended 
arteries.  From  the  foregoing  it  is  evident  that  the  gland  is 
not  exerting  itself  most  at  the  time  the  secretion  is  actively 
pouring  out,  but  that  the  real  constructive  period  of  activity 
is  the  one  between  such  times  of  flow,  the  period  during 
which  the  specific  element  is  gradually  built  and  stored  up. 
It  was  pointed  out  that  the  cerebro-spinal  nerve  seems 
wholly  concerned  with  the  water  and  the  salt  transudations, 
and  the  sympathetic  nerve  wholly  with  the  production  of 
the  specific  elements.  While  this  is  in  the  main  true,  there 
are  physiologists  who  believe  that  the  cerebro-spinal  nerve 


GLANDS,  GENERAL  PHYSIOLOGY  OF  SECRETION.   263 

also  exerts  a  slight  influence  in  the  production  of  the 
specific  element,  and,  on  the  other  hand,  that  the  sympa- 
thetic nerve  to  some  extent  exerts  an  influence  on  the 
secretion  of  the  water.  While  such  a  condition  of  things  is 
not  at  all  improbable,  experiments  on  glands  such  as  the 
one  just  described  clearly  demonstrate  that  in  the  main 
cerebro-spinal  nerves  govern  transudation,  the  function  of 
which  is  to  wash  out  the  specific  elements  when  such  are 
produced,  while  the  sympathetic  nerve  is  concerned  in  the 
production  of  these  specific  elements  themselves. 

So  far  there  has  been  considered  only  the  general  phy- 
siology of  secretion;  that  is,  those  phenomena  which  are 
common  to  all  glands.  The  special  physiology  of  the  in- 
dividual glands  is  reserved  for  a  detailed  discussion,  when 
these  glands  are  treated  in  connection  with  their  special 
functions. 


CHAPTER  XII. 


THE  DIGESTIVE  ORGANS  AND  THEIR 
ANATOMY. 

In  the  discussions  in  the  preceding  chapters  the  blood 
was  made  the  source  of  all  of  the  elements  needed  for  the 
tissues  or  secreted  by  the  glands.  In  the  chapter  on  respi- 
ration alone  was  it  pointed  out  that  in  turn  the  blood  derived 
its  source  of  oxygen  from  the  air,  and  that  it  derived  its 
supply  of  carbon  dioxide  from  the  tissues.  In  several  chap- 
ters there  is  now  to  be  pointed  out  in  what  manner  the 
blood,  which  is  the  medium  between  the  external  world  and 
the  tissues  of  the  body,  derives  its  supply  to  enable  it  in 
turn  to  supply  the  tissues. 

The  necessity  for  such  a  food  supply  is  entirely  too  evi- 
dent to  need  further  comment.  An  organ  stops  work  soon 
after  its  supply  of  blood  is  cut  off.  But  the  blood  is  in  no 
sense  a  living  tissue;  has  no  vitality  of  its  own;  is,  as  far 
as  the  tissues  are  concerned,  a  foreign  body;  is  nothing 
more,  in  short,  than  the  circulating  store-house  out  of 
which,  as  it  passes  along,  the  hungry  tissues  may  pick  up 
what  they  need  for  their  own  life.  To  cut  the  nutritive 
value.of  the  blood  down  below  a  certain  average  composition, 
or  to  put  into  the  blood  injurious  substances  will  at  once  re- 
act upon  the  tissues  which  derive  their  supplies  from  it. 
But  there  are  very  few  bodies  which  can  at  once  be  carried 
by  the  blood  and  serve  as  nourishment  for  the  live  tissues. 
Nearly  all  foods  are  in  a  solid  state,  and  in  this  condition 
they  are  unable  to  pass  into  the  circulation.  Even  many 
foods  in  a  liquid  condition  to  begin  with,  are  nevertheless 
not  available  as  foods  when  directly  placed  in  the  blood. 
Thus,  the  albumen  of  an  egg,  certainly  one  of  the  most 
nutritious  of  foods,  is  to  some  extent  poisonous  when  in- 
(264) 


DIGESTIVE    ORGANS    AND    THEIR    ANATOMY.  265 

jected  directly  into  the  blood-vessels,  and  is  not  utilized  at 
all  as  nourishment. 

Then  again,  the  vitality  of  the  tissues  depends  largely 
upon  the  constancy  and  permanency  of  the  blood  supply, 
and  to  place  at  once  into  the  blood  stream  varying  quanti- 
ties and  diverse  kinds  of  foods  would  react  at  once,  and  ma- 
terially interfere  with  the  normal  and  continued  activity  of 
the  cells.  To  transform  foods  and  change  them  into  sub- 
stances which  may  be  carried  by  the  blood  and  utilized  by 
the  tissues,  there  is  provided  by  the  body  one  of  the  most 
extensive  and  complicated  systems,  familiarly  termed  the 
alimentary  system  or  digestive  apparatus.  Before  noticing 
how  the  foods  are  affected  and  in  what  manner  they  are  pre- 
pared for  the  blood,  it  is  necessary  to  become  acquainted 
with  the  anatomy  of  this  system  itself. 

THE  MOUTH. 

'  The  mouth  serves  as  the  entrance  place  for  not  only  the 
solid  and  liquid  foods,  but  also  for  the  gaseous  food,  the 
oxygen  of  the  air,  a  food  in  no  less  sense  than  bread  and 
butter.  However,  in  the  mouth  the  solid  and  liquid  foods 
are  carried  to  the  pharynx  and  gullet  and  into  the  stomach, 
while  the  gaseous  food  in  the  manner  already  described,  is 
carried  to  the  lungs.  The  lung  is  in  no  far-fetched  sense, 
then,  an  adjunct  of  the  alimentary  canal,  intended  to  digest 
that  food  which,  on  account  of  its  gaseous  condition,  does 
not  need  the  action  of  further  juices  to  prepare  it  for  ab- 
sorption. Leading  out  of  the  mouth  are  six  openings:  The 
two  posterior  nares,  connected  with  the  nose  and  serving  as 
passage-ways  for  the  air ;  two  Eustachian  tubes  leading  from 
the  back  of  the  mouth  to  the  ear,  and  to  be  described 
further  in  the  chapter  on  hearing;  the  pharynx,  leading  into 
the  gullet,  and  in  front  of  the  pharynx,  the  larynx,  or  voice- 
box  leading  to  the  trachea.  While  the  mouth,  tongue  and 
teeth  figure  in  an  integral  way  in  the  formation  of  speech, 
we  are  concerned  here  only  with  their  digestive  function. 

This  is  mainly  the  process  of  mastication,  made  possible  by 


266  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

the   presence  of   the  teeth  for  crushing  the  food   and  the 
tongue  for  manipulating  it  during  this  act. 

1.     THE  TEETH. 

Arranged  in  a  single  row  in  both  upper  and  lower  jaw 
are  the  teeth.  These  appear  first  as  a  temporary  set  about 
the  sixth  or  seventh  month  and  disappear  at  about  the  sixth 
or  seventh  year.  This  temporary  set  is  usually  called  the 
milk  dentition  for  evident  reasons.  It  is  at  once  followed 
by  a  permanent  set,  which  consists  of  thirty-two  individual 
teeth,  sixteen  above  and  sixteen  below.  Taking  half  of 
either  row,  the  two  in  front  are  called  the  incisors,  or  cut- 
ting teeth.  They  have  a  peculiar  chisel-like  edge,  making 
them  specially  adapted  for  cutting.  These  are  followed 
by  a  single  canine  tooth,  sometimes  called  the  eye-tooth  (in 
upper  jaw) .  The  name  canine  is  derived  from  the  fact  that 
this  tooth  is  especially  developed  in  the  carnivorous  ani- 
mals, and  is  there  used  for  tearing  the  food.  To  make  rl 
more  efficient  as  a  tearing  tooth  in  the  carnivora,  it  is  fre- 
quently much  longer  than  the  others;  in  fact,  sometimes  so 
long  as  project  from  the  mouth.  The  canine  is  followed  by 
two  premolars,  called  bicuspids  also,  from  the  fact  that  they 
have  but  two  fangs.  The  premolars  are  the  teeth  of  the 
permanent  set  which  have  replaced  the  molars  of  the  milk 
dentition.  Following  the  two  premolars  we  have  three 
molar  teeth  not  represented  at  all  in  the  temporary  set. 
These  molars  are  called  tricuspids  also,  from  the  fact  that 
they  have  three  fangs.  Both  the  premolars  and  the  molars 
are  especially  adapted  for  the  crushing  and  grinding  of 
foods.  The  last  premolar  does  not  usually  appear  until  from 
the  eighteenth  to  the  twenty-fifth  year,  and  has  for  this 
reason  been  called  the  "wisdom"  tooth. 

There  is  a  marked  analogy  between  the  teeth  of  man  and 
those  of  many  of  the  lower  mammals,  but  modifications  of 
this  typical  arrangement  are  met  with  in  certain  classes  of 
animals.  Thus,  in  animals  like  the  sheep  and  cow,  which  are 
obliged  to  pick  the  grass  very  closely,  the  upper  front  teeth 


DIGESTIVE   ORGANS   AND   THEIR   ANATOMY. 


267 


are  missing  and  the  lower  teeth  strike  against  an  upper  pad. 
In  the  class  of  rodents  or  gnawers,  which  includes  such 
forms  as  the  rat  and  the  squirrel,  the  incisors  are  remark- 
ably developed.  They  keep  growing  throughout  life,  and 
have  to  be  kept  short  by  being  worn  off  against  each 
other.  In  this  way  these  teeth  are  kept  continually  very 
sharp.  It  not  infrequently  happens  that  such  a  rodent 

breaks  off  one  of  the 
incisors,  in  which  case 
the  opposite  incisor  no 
longer  worn  away, 
grows  indefinitely,  and 
may  finally  grow 
around  back  into  the 
head  of  the  animal  and 
cause  its 'death.  ;,  : 

The  Structure  of  a  Tooth. 

The  typical  tooth, 
such  as  a  canine,  for 
instance,  consists  of 
three  parts — the  fang 
imbedded  in  the  jaw, 
the  neck,  and  the 
crown  projecting  from 
the  gums.  If  such  a 
tooth  be  cut  in  two 
longitudinally  there  is 
disclosed  in  the  center 
a  large  cavity  known 
as  the  "pulp"  cavity 
and  opening  to  the  ex- 
terior through  the 
fangs.  At  these  points 

^ig.  100.— VERTICAL  SECTION  OFAPREMOLAR  OF  THE    nerves    and    blood-VCS- 

CAT.  (After  waideyer.)  sels  enter  the  pulp  cav- 

c,  pulp  cavity;  J,  enamel;  2,  dentine;    3,  cement;     .  ^,  .      -,       -, 

4,  dental  periosteum;  5,  bone  of  lower  jaw.  ity.      The  main  body  of 


268 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


the  tooth  is  made  of  a  substance  known  as  dentine,  or  ivory. 
In  composition  it  is  not  very  different  from  bone,  but  his- 
tologically  it  is  not  the  same.  Dentine  possesses  neither 
Haversian  canals  nor  lacunae,  and  so,  of  course,  has  no 
osteoblasts  imbedded  in  its  substance.  Running,  however, 
from  the  pulp  cavity  outward  and  permeating  the  dentine 
everywhere  are  fine  tubules,  each  about  Toinr  of  an  inch 
in  diameter.  Near  the  outside  of  the  dentine  these  tubules 
frequently  open  into  large  irregular  spaces  known  as  inter- 
globular  spaces.  The  function  of  these  spaces  is  not  known. 


Fig.  101.— SECTION  OF  FANG  OF  HUMAN  CANINE.    (After  Waldeyer.) 
1,  cement,  with  lacunae  and  lamellae;   2,  layer  of  interglobular  spaces;   3,  dentinal 


tubules. 


Through  these  dentinal  tubules,  for  a  little  distance  at  least, 
arms  of  dentinoblasts  extend,  which  are  immediately  con- 
cerned with  the  growth  and  repair  of  the  dentine.  These 


DIGESTIVE    ORGANS   AND   THEIR   ANATOMY. 


269 


dentinoblasts  lie  next  to  the  dentine  in  the  pulp  cavity  and 
are  probably  not  essentially  different,  except  in  position, 
from  the  osteoblasts  in  bone.  The  reason  for  the  absence 
of  lacunae  and  Haversian  canals  in  the  ivory  is  of  course 
apparent.  Such  a  system  of  holes  and  spaces  would  materi- 
ally interfere  with  the  hardness  and  solidity  of  dentine  and 
so  make  it  much  less  serviceable  in  the  crushing  of  foods. 

In  the  fang  this  dentine  is  covered  over  by  a  thin 
layer  of  cement  by  means  of  which  it  is  bound  to  the 
jaw-bone.  This  cement  is  nothing  but  ordinary  bone, 
and  as  such  contains  lacunae  and  not  infrequently  Haversian 
canals. 

On  the  crown  the  dentine  is  covered  over  with  a  coat- 
ing of  an  exceedingly  hard  substance  known  as  enamel. 
This  is  totally  different  from  the  dentine  both  in  structure 
and  in  origin.  The  dentine  is  essentially  bone,  but  the 
enamel  is  derived  from  the  skin,  like  the  nails  of  the  fin- 
gers. There  has,  however,  been  such  a  mineral  deposition 


Fig.  102.— ENAMEL  PRISMS.    (After  Kb'lliker.) 

A,  fragments  and  single  columns  of  enamel;  B,  surface  view,  showing  the  hexagonal 
ends  of  the  prisms. 

in  these  epidermal  cells  as  to  transform  them  into  the  hard- 
est substance  in  the  body.  In  structure  the  enamel  con- 
sists of  more  or  less  hexagonal  prisms  arranged  vertically 


270  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

with  reference  to  the  stress  to  which  they  are  subjected. 
In  a  perfectly  new  tooth  which  has  not  suffered  any  abra- 
sion the  enamel  is  covered  over  with  a  slight  cuticle,  also 
of  skin  origin,  which,  however,  at  once  disappears  when 
the  tooth  is  put  to  hard  use. 

Hygiene. 

While  in  the  dentine  of  a  tooth  a  slight  growth  and  re- 
pair may  be  possible,  it  is  not  possible  to  remedy  a  defect 
in  the  tooth  when  it  assumes  at  all  large  dimensions,  while 
of  course  a  cracking  or  loss  of  the  enamel  is  at  once  irre- 
parable. As  the  teeth  are  almost  wholly  of  a  mineral  na- 
ture they  are  subject  to  the  action  of  acids,  and  as  in  the 
decomposition  of  foods  various  organic  acids  are  produced 
there  is  a  constant  corroding  action  going  on  which  may 
finally  destroy  the  teeth.  While  the  enamel  is  over  them, 
this  corroding  action  is  largely  prevented,  but  as  soon  as 
the  hard  enamel  gives  way  and  the  acids  have  direct  access 
to  the  softer  dentine  beneath,  the  corroding  influence  pro- 
ceeds more  rapidly.  This  explains  in  the  clearest  way  the 
necessity  for  absolute  cleanliness  of  teeth  in  order  to  pre- 
serve them. 

Around  the  teeth,  sometimes  even  in  spite  of  good  care, 
there  is  formed  a  deposit  familiar  as  tartar.  This  is  not  wholly 
derived  from  bits  of  food  which  have  not  been  removed,  but 
the  tartar  is  mainly  a  deposit  of  lime  salts  derived  from  the 
saliva.  In  ordinary  saliva  lime  salts  are  present,  and  as  the 
teeth  are  continually  bathed  in  such  a  lime  solution  a  de- 
position of  these  salts  around  the  teeth  goes  on  and  so  gives 
rise  to  the  crusty  tartar.  This  act  of  deposition  is  illus- 
trated in  the  lime  crusts  which  form  on  the  inside  of  kettles 
or  boilers  in  which  hard  water  has  been  continually  kept. 
When  such  tartar  is  merely  a  pure  lime  deposit  it  is  pos- 
sible that  it  may  interfere  in  no  way  with  the  teeth,  except, 
possibly,  to  irritate  the  gums,  when  these  are  pressed  down 
on  the  tartar  underneath  them  and  so  produce  bleeding,  but 
most  frequently  there  is  deposited  along  with  this  tartar  and 


DIGESTIVE   ORGANS   AND   THEIR   ANATOMY. 


271 


in  it,  much  decayed  food  material,  in  which  case  the  tartar 
itself  with  these  decaying  impurities  in  it  becomes  a  source 
of  infection  and  needs  immediate  removal. 

The  hygiene  of  the  teeth  forms  such  an  integral  part  of 
a  person's  general  sense  of  order  and  cleanliness  that  it 
would  be  entirely  out  of  place  to  comment  further  on  it  in 
this  connection. 

The  Development  of  the  Teeth. 

As  pointed  out  previously,  the*  teeth  when  once  fully 
formed  are  not  able  to  grow  or  repair  themselves  in  any  ma- 
terial way.  This  is  absolutely  true  of  the 
enamel.  After  that  has  been  formed  in 
the  first  appearance  of  the  tooth,  it  is 
never  possible  to  be  replaced  later.  How- 
ever, with  the  dentine  a  slight  repairing 
action  may  be  noticed.  If,  for  instance, 
on  the  crown  or  neck  of  the  tooth  where 
the  enamel  has  been  removed,  the  dentine 
has  been  worn  away  and  a  cavity  so  re- 
sulted, there  is  not  infrequently  deposited 
in  the  pulp  cavity  on  the  dentine  in  a 
position  corresponding  exactly  with  the 
corroded  place  on  the  outside  a  new  bit 
of  bone-like  dentine  which  serves  to  coun- 
teract, to  some  extent  at  least,  the  corro- 
sive action  on  the  outside.  Even  the 
dentinal  tubules  which  extend  into  the 
dentine  so  softened  or  corroded  become 

Fig.  103.  —  LONGITUDINAL    o11J.1 

SECTION  OF  AN  INCISOR  filled  with  calcareous  depositions  and  the 

rT  GD™TT'R;  tooth  so  becomes  firmer  and  consequently 
AND  /,  POINTS  CORRE-  more   resistant  to  decay.     Reference  to 

,«  .  ...  .-,  ,      . 

the  accompanying  diagram  will  explain 
this>  The  cement  of  the  teeth  is  within 
certain  limits  easily  replaced.  It  is  prac- 
tically nothing  but  bone  and  is  secreted  by  a  kind  of  peri- 
osteum which  covers  the  jaw-bone  and  which  dips  into  the 


SPONDING   TO  PLACES  OF 

DENUDED  DENTINE  ON 
THE  EXTERIOR.    (After 

Salter.) 


272 


STUDIES   IN   ADVANCED    PHYSIOLOGY. 


sockets  in  which  the  teeth  are  held.  It  not  infrequently 
happens  that  teeth  quite  loose  are  in  a  short  time  again 
firmly  set  in  their  places. 

Origin  of  the  Enamel. — The  manner  in  which  the  teeth 
arise  originally  may  be  tolerably  easily  understood  by  ex- 
amining a  section  from  the  jaw-bone  of  a  foetus,  in  which 
the  rudiment  of  the  teeth  are  just  making  their  appearance. 
In  such  an  examination  it  will  be  found  that  the  first  indi- 
cation of  teeth  is  a  pitting  in  of  the  epithelium  of  the 
mouth  (the  skin)  in  the  form  of  a  groove,  which  occupies 
about  that  position  on  the  jaw  where  later  the  row  of  teeth 
is  to  appear.  This  groove  of  epithelial  cells  grows  down 
into  the  substance  of  the  jaw,  and  from  this  groove  there 
grow  out  little  side  projections  which  soon  begin  to  shape 
themselves  into  the  forms  of  the  crowns  of  the  intended 
teeth.  This  epithelial  outgrowth  produces  the  enamel  of 
the  teeth,  so  that  this  part  of  it  appears  in  a  developing 


^ 


Xg. 


(After 


Fig.  104.— SECTION  THROUGH  A  DEVELOPING  MILK  MOLAR  OF  A  HUMAN  EMBRYO. 

Rose.) 

L.  E.  L.,  labiodental  lamina;  M.E.,  the  epithelium  of  the  mouth;  Z.L.,  dental 
lamina,  spreading:  out  at  P.p.  to  form  the  enamel  cap  of  the  future  bicuspidate  tooth ; 
Z.  S.,  the  condensed  tissue  forming  the  dental  sac. 

tooth  some  time  before  the  body  of  the  tooth,  the  dentine, 
arises.  The  cells  of  the  lowest  row  of  these  lateral  out- 
growths become  columnar  and  elongated  and  form  the  enamel 
prisms.  According  to  some  anatomists  these  hexagonal 


DIGESTIVE   ORGANS   AND   THEIR   ANATOMY.  273 

prisms  result  from  a  direct  calcification  of  these  columnar 
cells  themselves,  and  in  this  way  they  account  for  the  hex- 
agonal shape  of  the  prisms.  Other  anatomists  hold  that  the 
enamel  prisms  are  formed  from  secretions  which  these  cells 
produce  at  one  end.  It  is  impossible  to  determine  just 
which  of  these  two  views  is  correct,  the  probability  being 
that  the  cells  themselves  become  hardened  into  the  prisms, 
just  as  in  the  case  of  the  finger  nail  similar  epithelium  cells 
become  hardened  into  these  horny  structures.  The  upper 
layers  of  cells  of  this  lateral  outgrowth  become  changed  into 
the  enamel  cuticle  which  was  referred  to  as  covering  a  per- 
fectly new  tooth. 

Formation  of  Dentine. — As  soon  as  the  enamel  crown 
begins  to  arise  in  the  way  just  indicated,  cells  appear  im- 
mediately underneath  it,  which  begin  to  deposit  dentine 
next  to  the  enamel.  These  cells,  called  dentinoblasts,  or 
by  others  odontoblasts,  secrete  a  matrix  which  hardens  at 
once  into  the  ivory.  In  this  matrix  these  cells  extend  pro- 
toplasmic processes  which  become  imbedded  in  the  dentine, 
and  which  in  the  fully  formed  tooth  are  the  protoplasmic 


Fig.  105. — SECTION  OF  DEVELOPING  DENTINE  FROM  AN  INCISOR  OF  A  YOUNG  RAT.    (After 

Schafer.) 

a,  outer  layer  of  fully  formed  dentine ;  &,  soft  matrix,  with  a  few  nodules  of  calcareous 
matter  already  in  it ;  c,  odontoblasts  with  arms  extending  into  the  dentine ;  d,  pulp  cavity 
with  contained  pulp. 

processes  lying  in  the  dentinal  tubules.  These  dentino- 
blasts, however,  do  not  wall  themselves  in  as  in  the  case  of 
bone,  but  always  remain  outside  of  the  dentine  in  the  pulp 
cavity.  Thus  the  dentine  surrounding  one  or  more  den- 
tinal tubules  from  the  enamel  entirely  down  to  the  pulp 
18 


274  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

cavity  is  the  product  of  a'  single  odontoblast.  In  an  adult 
tooth  these  odontoblasts  in  reduced  number  may  still  be 
found  next  to  the  pulp  cavity. 

The  growth  of  a  tooth  begins  with  the  crown  and  ex- 
tends to  the  fang.  As  this  growth  proceeds  downwards  the 
crown  is  gradually  pushed  upwards  and  so  soon  appears 
above  the  gums.  While  the  tooth  is  thus  developing  the 
jaw-bone  around  it  is  also  developing,  and  so  when  the 
tooth  appears  it  finds  itself  firmly  placed  in  its  bony  socket. 
In  the  case  of  the  milk  dentition  the  cement  which  forms 
seems  to  be  removed  by  the  action  of  osteoclasts,  and  so 
these  teeth  soon  drop  out  and  are  replaced  by  the  perma- 
nent set.  These  permanent  teeth  develop  in  a  way  perfectly 
analogous  to  that  of  the  milk  dentition.  From  the  epi- 
thelium groove  from  which  the  lateral  enamel  outgrowths, 
or  milk  teeth  arise,  secondary  outgrowths  arise  which  are 
later  on  to  form  the  enamel  coverings  of  the  permanent 
teeth.  These  epithelial  cells  concerned  in  the  formation 
of  the  enamel  are  called  adamantoblasts .  The  epithelium 
groove  of  course  soon  disappears  after  the  lateral  out- 
growths from  it  have  resulted,  and  no  vestige  of  it  remains 
in  the  adult  jaw. 

2.     THE  TONGUE. 

The  tongue  is  a  muscular  organ  with  its  base  attached  to 
the  floor  of  the  mouth  and  to  the  hyoid  bone,  and  covered 
over  with  a  sensitive  mucous  membrane.  On  this  mucous 
membrane  there  are  developed  three  kinds  of  papillae. 
Scattered  all  over  the  tongue  are  small  pointed  projections 
known  as  the  filliform  papilla.  They  are  not  very  well 
developed  in  man,  but  are  in  many  of  the  lower  animals. 
The  intense  roughness  of  a  cow's  tongue  is  due  to  these 
filliform  papillae,  while  with  many  of  the  carnivora  these 
papillae  enable  them  to  scrape  the  bones  and  remove  from 
them  by  their  rasping  action  all  shreds  of  flesh.  They 
function  mainly  in  man  to  give  the  tongue  a  certain  rough- 
ness so  that  it  may  more  readily  manipulate  the  food  in  the 
act  of  mastication  and  in  swallowing. 


DIGESTIVE   ORGANS    AND   THEIR   ANATOMY. 


275 


Not  so  numerous  as  the  filliform,  but  scattered  over 
almost  the  entire  tongue  are  somewhat  larger,  blunter 
papillae  known  as  the  fungiform.  The  position  of  these 


Fig.  106.— SURFACE  VIEW  OF  THE  HUMAN  TONGUE.    (After  Sappey.) 
1,  2,  circumvallate  papillae;  3,  fungiform  papillae;  4,  filliform  papillee;  5,  oblique  folds; 
6,  mucous  and  lymphoid  follicles ;  7,  tonsils;  8,  tip  of  epiglottis ,  9,  median  glosso-epiglot- 
tic  fold. 

papillae  may  easily  be  recognized  on  the  tongue  in  the  red- 
dish spots  which  mark  the  tip  of  the  tongue  at  times. 
Nerves  of  taste  are  distributed  to  these,  and  their  function 
is  no  doubt  in  connection  with  this  sense. 


276  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

But  the  sense  of  taste  is  most  acute  on  the  third  form  of 
papillae  known  as  the  circumvallate  papilla.  These  are 
the  largest  of  all,  and  may  readily  be  seen  on  the  back  of 
the  tongue,  where  they  are  arranged  in  a  V-shaped  way, 
with  the  open  end  of  the  V  forwards.  There  are  about  a 
dozen  individual  circumvallate  papillae  in  this  V.  These 
papillae  do  not  project  materially  above  the  surface  of  the 
tongue,  but  seem  to  be  set  down  in  the  mucous  membrane 
of  the  tongue,  being  surrounded  with  a  kind  of  moat  not 
unlike  the  moat  of  mediaeval  castles.  In  the  walls  of  this 
moat,  both  outer  and  inner,  are  found  special  taste  bulbs, 
which  will  be  described  later,  and  which  seem  especially 
concerned  in  the  sensation  of  taste.  The  presence  of  these 
acute  taste  bulbs  at  the  base  of  the  tongue  explains  the 
familiar  fact  that  foods  are  most  sapid  at  the  instant  they 
are  being  swallowed.  Possibly  the  explanation  of  this  is 
that  with  animals  at  least,  and  possibly  with  man,  it  serves 
as  an  inducement  to  the  swallowing  of  food. 

On  the  back  of  the  tongue  just  at  the  pillars  of  the  throat 
are  the  tonsils.  These  are  lymphatic  glands  about  the  size 
of  a  small  bean,  and  apart  from  their  general  function  as 
lymphatic  glands  they  seem  to  serve  in  no  special  way  in 
their  position  on  the  tongue.  The  mucous  membrane  cov- 
ering the  tonsils  is  deeply  pitted  at  these  points,  and  the 
position  of  the  tonsils  may  be  readily  recognized  by  these 
mucous  pits. 

When  by  the  action  of  the  tongue  and  pharynx  the  food 
is  swallowed  it  is  carried  over  the  opening  leading  into  the 
larynx  by  the  epiglottis,  a  cartilaginous  flap  which  at  the 
moment  of  deglutition  bends  down  and  covers  the  passage- 
way to  the  lungs.  The  food  is  thus  carried  over  the  epi- 
glottis and  is  seized  by  the  involuntary  muscles  of  the  gullet 
or  oesophagus  and  so  sent  to  the  stomach. 

3.     THE  GULLET    OR    (ESOPHAGUS. 

The  alimentary  canal,  although  more  or  less  arbitrarily 
divided  into  the  gullet,  stomach,  and  small  and  large  intes- 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY. 


277 


tines,  is  in  reality  but  a  single  continuous  tube  with  but 
slight  local  variations.  For  this  reason  a  description  of  the 
coats  of  the  alimentary  canal  will  apply  almost  equally  well  to 

all  parts  of  its  course.  The  alimen- 
tary canal  is  made  up  of  four  dis- 
tinct coats.  On  the  outside  there 
is  a  serous  coat,  which  is  in  the 
oesophagus .  a'  reduplication  of  the 
pleura,  and  in  the  abdomen  a  redu- 
plication of  the  peritoneum.  Next 
to  this  thin  serous  coat  is  a  thick 
muscular  coat  consisting  of  two  por- 
tions ;  an  outer  portion  in  which  the 
fibres  run  longitudinally,  and  an 
inner  portion  in  which  the  fibres 
run  circularly.  It  is  not  necessary 
to  repeat  that  these  muscle  fibres 
are  of  the  plain  involuntary  variety. 
Between  the  longitudinal  and 
circular  muscles  there  run  numer- 
ous blood-vessels  to  supply  this 
coat,  and  there  occurs,  also,  a  com- 
plex network  of  ganglia,  and  nerve 
fibres  known  as  the  plexus  of  A  tier- 
bach.  From  this  plexus  the  mus- 
cles are  directly  innervated.  Next 
to  the  muscular  coat  is  a  sub-mu- 
cous coat  consisting  largely  of  are- 

P  ig.  107.— DIAGRAMMATIC  SECTION 

THROUGH  THE  COATS  OF  THE    olar    tissue,  with   contained  blood- 

STOMACH.     (After  Mall.)  i  j    -i  1      ,•  j 

vessels  and  lymphatics  and  serving 

m,  mucous  membrane;  d,  duct  . 

of  gastric  giand;  m.  m.,  muscular  mainly  to  bind  down  to  the  muscu- 

lar  coat  the  large  mucous  coat.  In 
this  sub-mucous  coat  there  is  a 
second  well-developed  network  of 

ganglia  and  nerve  fibres  known  as  the  plexus  of  Meissner. 

From  this  plexus  the  mucous  membrane  and  its  glands  are 

innervated.     The  last,  and  in  some  ways  the  most  essential 


coat  of  mucous  membrane;  s.  m., 
submucous  coat;  c.  m.,  circular 
muscles;  Lm,,  longitudinal  mus- 
cles; s.,  serous  coat. 


278 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


coat,  is  the  mucous  coat,  which  consists  of  two  portions:   A 
portion  next  to  the  sub-mucous,  largely  fibrous,  containing 


Fig.  108.— THE  PLEXUS  OF  MEISSNER.    (After  Cadiat.) 

a,  a,  ganglia;  6,  6,  network  of  nerves;  c,  a  small  blood-vessel;  d,  a  nerve  passing  to 
muscular  layer  of  mucous  membrane,  or  to  the  villi. 

numerous   blood-vessels,   lymphatics,   and   nerves,   and    an 
outer  covering  of  epithelium  cells. 

In  the  gullet  there  is  practically  no  modification  of  this 
typical  arrangement.  The  epithelium  of  the  mucous  mem- 
brane differs,  however,  from  that  of  the  stomach  and  intes- 
tines in  being  many-layered.  However,  close  to  the  junction 
of  the  oesophagus  with  the  stomach  these  layers  are  reduced, 
and  in  the  stomach  and  intestines  but  a  single  layer  remains. 

4.     THE  STOMACH. 

The  stomach  is  but  a  local  dilatation  of  the  alimentary 
tract,  and  serves  as  a  temporary  halting  place  for  the  diges- 


DIGESTIYK    ORGANS    AND   THEIR   ANATOMY. 


279 


tion  of  food.  The  shape  of  the  stomach  is  at  once  evident 
from  the  accompanying  diagram.  It  lies  mainly  to  the  left 
side  of  the  body,  being  displaced  from  a  median  position 
by  the  large  liver  which  occupies  the  corresponding  right 
position.  The  portion  next  to  the  oesophagus  is  the  cardiac 
portion,  that  portion  connected  with  the  intestine,  the  py- 
loric  portion.  The  upper  curvature  is  spoken  of  as  the  small 


Fig.  109.— THE  HUMAN  STOMACH. 

A,  cardiac  end;  c,  fundus;  P,  sphincter  muscle,  pyloric  end;  lines  indicate  longitudi- 
nal muscle  fibres. 

curvature,  the  lower  as  the  large  curvature.  The  big  sac- 
like  dilatation  formed  by  the  large  curvature,  called  the  fun- 
dus of  the  stomach,  varies  greatly  in  size  with  the  varying 
amount  of  food  taken.  In  a  not-too-distended  stomach  the 
dimensions  are  about  nine  or  ten  inches  in  its  long  diam- 
eter, and  from  five  to  seven  inches  in  its  short  diameter. 
The  outer  or  serous  coat  is  a  part  of  the  peritoneum  which 
lines  the  abdominal  cavity,  and  which  is  folded  around  the 
stomach  as  the  mesentery.  At  the  front  of  the  stomach, 
however,  this  fold  is  extended  downwards  over  the  intes- 
tines as  a  large  covering  or  apron,  and  is  called  the  great 
amentum.  This  omentum  frequently  becomes  the  seat  of 
fatty  deposition,  and  no  doubt  materially  serves  to  protect 
the  underlying  viscera  from  changes  of  temperature. 

The  muscular  coat  is  a  little  modified  from  the  typical 
arrangement,  there  being  three  instead  of  two  parts.     The 


280 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


outer  muscle  fibres  run  longitudinally.  The  middle  coat  is 
circular,  but  inside  of  the  middle  coat  there  is  a  third  coat 
not  quite  complete,  in  which  the  direction  of  the  fibres  is 
oblique.  This  especial  development  of  the  muscles  is  no 
doubt  intended  to  make  possible  the  movements  of  the 
stomach  which  accompany  gastric  digestion. 

The  sub-mucous  coat  binds  down  to  the  muscular  coat 
the  large  glandular  mucous  coat  of  the  stomach.  This 
mucous  coat  is  covered  on  the  inside  with  a  single-lavered 


Fig.    110. — A     CARDIAC     GLAND     FROM     THE  Fig.     111. — A   GASTRIC   GLAND   STAINED    BY 


DOG'S  STOMACH.     (After  Klein  and  No- 
ble Smith.) 

d,  duct  of  gland;   b,  base  or  fundus;  c, 
ordinary  peptic  cell;  pt  oxyntic  cell. 


CHROMATE  OF  SILVER,  SHOWING  THE 
EXTENSION  OF  THE  LUMEN  INTO  THE 
NETWORKS  SURROUNDING  THE  OXYN- 
TIC CELLS,  FOR  THE  EXIT  OF  THK  ACID 
SECRETION  OF  THESE  CELLS.  (After 

Miiller.) 


epithelium,  which  everywhere  dips  down  into  the  mucous 
coat  and  forms  pits,  or  more  properly  speaking,  tubular 
glands.  These  glands  are  the  gastric  glands.  The  epi- 
thelial lining  of  the  inside  of  the  stomach  is  continued  into 


DIGESTIVE    ORGANS    AND   THEIR   ANATOMY.  281 

these  glands,  and  forms  the  secreting  cells  of  the  same. 
These  cells  lining  the  glands  are  spoken  of  as  the  chief  cells, 
or  on  account  of  the  fact  that  they  secrete  pepsin  they  are 
called  peptic  cells.  During  the  resting  periods  of  the  stomach 
these  cells  become  filled  with  pepsinogen  granules,  which 
when  digestion  commences,  are  changed  into  pepsin  and 
poured  into  the  stomach  in  a  manner  indicated  in  detail  in 
the  preceding  chapter. 

But  in  the  gastric  glands  everywhere  except  near  the 
pyloric  end,  there  are  found  underneath  these  peptic  cells, 
scattered  here  and  there,  other  more  oval  cells  which  are 
called  oxyntic  cells.  This  name  is  derived  from  the  fact 
that  these  oxyntic  cells  produce  the  hydrochloric  acid  of  the 
gastric  juice.  Although  these  oxyntic  cells  seem  to  lie  un- 
derneath the  peptic  cells  and  not  to  connect  at  all  with  the 
lumen  of  the  gland,  special  histological  methods  show  that 
there  are  delicate  canals  leading  from  these  oxyntic  cells  in- 
to the  duct,  so  making  possible  the  easy  transfer  of  the 
hydrochloric  acid  into  the  stomach.  While  most  of  these 
gastric  glands  are  simply  tubular  glands  extending  the  depth 
of  the  mucous  coat,  it  not  infrequently  happens  that  two  or 
more  gastric  glands  may  have  a  common  duct. 

Both  the  mucous  and  the  sub-mucous  coat  of  the  stom- 
ach are  richly  supplied  with  blood-vessels  which  reach  the 
stomach  through  the  gastric  artery,  a  branch  of  the  cceliac 
axis.  The  stomach  is  supplied  with  both  cerebro-spinal  and 
sympathetic  nerves.  Branches  of  the  pneumogastric  go 
to  the  stomach  direct,  and  nerves  from  the  solar  plexus 
just  back  of  the  stomach  also  reach  it,  while  sympathetic 
nerves  run  mainly  to  the  gastric  arteries. 

5.     THE  SMALL  INTESTINE. 

The  alimentary  canal  is  continued  beyond  the  stomach  as 
the  small  intestine.  There  is  a  tolerably  sharp  demarca- 
tion between  the  pyloric  end  of  the  stomach  and  the  begin- 
ning of  the  intestine,  due  to  the  presence  of  an  especially 
developed  sphincter  muscle  at  the  pyloric  orifice,  which  is 


282  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

usually  closed, -and  opens  only  from  time  to  time  to  allow 
properly  digested  food  to  pass.  The  small  intestine  is 
much  coiled,  and  has  a  length  of  about  twenty  feet.  The 
coils,  however,  do  not  lie  superimposed  one  on  the  other  in 
the  abdominal  cavity,  but  are  all  suspended  in  mesenteric 
slings  from  the  back  bone.  This  suspension  not  only  keeps 
the  folds  from  resting  upon  each  other,  but  also  prevents 
them  from  being  relatively  displaced.  The  first  twelve 
inches  of  the  intestine  are  called  the  duodenum  (which 
means  twelve) ,  because  in  this  portion  of  the  intestine  but 
little  active  digestion  is  going  on,  the  mixture  of  the  foods 
with  the  pancreatic  juice  and  the  bile  taking  place  here. 

By  far  the  larger  portion  of  the  remainder  is  called  the 
jejunum )  while  the  final  third  is  spoken  of  as  the  ileiim. 
This  division  is  quite  arbitrary,  and  the  commencement  of 
the  ileum  is  roughly  stated  to  be  that  point  where  the  disin- 
tegration of  food  has  begun  to  reach  the  putrefactive  stage. 

The  structure  of  the  intestinal  walls  does  not  vary  very 
much  from  the  typical  four  coats.  On  the  outside  is  the 
serous  coat,  a  reduplication  of  the  peritoneum,  and  called 
the  mesentery.  In  these  folds  of  the  mesentery  the  loops 
of  the  intestines  are  of  course  supported,  and  through  these 
folds  blood-vessels,  nerves  and  lymphatics  reach  them. 
The  muscular  coat  consists  of  an  outer  longitudinal  and  an 
inner  circular,  between  which  are  the  nerve  plexus  of  Auer- 
bach  and  numerous  blood-vessels.  The  muscular  coat  is 
followed  by  the  submucous,  in  which  there  are  numerous 
blood  -  vessels  and  lymphatics  and  the  nerve  plexus  of 
Meissner.  The  submucous  is  followed  in  turn  by  the  mu- 
cous coat,  the  principal  coat  of  the  intestine.  This  mucous 
coat  shows  a  number  of  peculiarities.  In  the  first  place,  it 
is  even  in  a  fairly  distended  intestine  thrown  into  numer- 
ous transverse  folds  called  valvulcz  conniventes,  the  pur- 
pose of  which  is  to  afford  a  greater  secreting  surface,  and 
at  the  same  time  to  form  lateral  pouches  in  which  the  food 
will  be  detained  and  so  better  acted  upon  by  the  digestive 
juices.  Close  examination  of  the  mucous  membrane  shows 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY. 


283 


it  to  be  covered  with  fine  projections  not  entirely  unlike  the 
"pile"  on  velvet.    Examination  with  the  microscope  shows 


Fig.  112.— PORTION  OF  THE  SMALL  INTESTINE  TO  SHOW  THE  VALVUL.E  CONNIVENTES. 
(Brinton.) 

that  these  little  projections  are  finger-like  protrusions  of  the 
mucous  membrane.    These  are  called  the  ( 'villi, ' '  and  are  in 


Fig.  113.— SECTION  OF  A  HUMAN  INTESTINAL  MUCOUS  MEMBRANE,  SHOWING  THREE  COM- 
PLETE VILLI  AND  six  CRYPTS  OF  LJEBERKUHN.     (After  Bohm  and  v.  Davidoff.) 

an  integral  way  concerned  in  the  absorption  of  the   foods. 
Between  these  villi  and  dipping  down  into  the  mucous  mem- 


284 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


brane  are  small  glands  called  the  crypts  of  Lieberkuhn. 
The  epithelial  lining  that  covers  the  mucous  membrane  is 
one-layered.  This  epithelium  extends  down  into  the  crypts 
of  L,ieberkiihn  and  forms  in  them  the  secreting  cells.  It  is 
also  continued  over  the  villi.  A  single  villus,  therefore, 
consists  of  a  layer  of  epithelium  covering  the  fibrous  cen- 
tral portion,  through  which  run  numerous  blood-vessels, 
while  in  the  center  of  the  villus  there  is  a  single  large  lym- 
phatic called  here  a  lacteal.  The  rich  supply  of  blood- 
vessels to  such  a  villus  accounts  for  the  efficiency  of  these 
structures  in  the  process  of  absorption,  while  the  central 
lacteal  is  the  avenue  through  which  the  fats  reach  the  body 
in  a  manner  to  be  described  in  the  succeeding  chapter. 


Fig.  114.— INJECTED  VILLI  OF  THE  HUMAN  INTESTINE.     (After  Teichmann.) 
a.  b,  lacteals  (white);  c,  horizontal  lacteals;  d,  networks  of  blood-vessels  (dark). 

Nerves  and  bits  of  plain  muscular  tissue  distributed  through 
the  body  of  the  villus  also  occur.  These  bits  of  plain 
muscular  tissue  make  possible  the  slight  powers  of  con- 
traction which  are  said  to  materially  aid  in  their  absorptive 
capacity. 

The  villi  extend  from  the  beginning  of  the  duodenum 
through  the  length  of  the  small  intestine.  The  crypts  of 
Ivieberktilm  between  them  have  a  similar  distribution.  In 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY. 


285 


the  duodenum  there  are  found  additional  glandular  struc- 
tures called  the  glands  of  Brunner.  They  are  somewhat 
longer  tubular  glands  which  extend  down  to  the  submucous 
coat.  The  ducts  of  these  open  into  the  intestine  between 
the  crypts  of  Lieberkuhn.  The  glands  of  Brunner  have  no 
especial  function,  and  are  in  all  probability  but  glands 
similar  to  the  peptic  glands  of  the  stomach,  which  have 
reached  down  into  the  commencement  of  the  intestine. 
They  secrete  small  amounts  of  pepsin  which,  however,  in 
the  intestine  are  of  no  value  at  all.  We  may  therefore  speak 
of  these  glands  of  Brunner  as  ordinary  gastric  glands 
which  have  been  continued  beyond  the  pyloric  orifice.  The 
crypts  of  L,ieberkiihn  are  similar  to  the  gastric  glands,  but 
are  much  shallower  and  never  possess  added  oxyntic  cells. 
Of  course  the  secretion  which  they  produce,  the  intestinal 
juice,  differs  materially  from  the  gastric  juice. 

As  the  small  intestine  is  to  a  much  greater  extent  than 
the  stomach  the  seat  of   absorption,  we  find  that  the  walls 


Fig.  115. — SECTION  OF  AN  INJECTED  ILEUM,  SHOWING  THE  INJECTED  LACTEALS,  VILLI, 

TWO  PATCHES  OF  PEYER,  ETC.      (After  Frey.) 

a,  a,  a,  villi;  6,  crypts  of  I,ieberkuhn;  c,  muscular  layer  of  mucous  membrane;  d,  d, 
e,  e,  patches  of  Peyer;  f,  g,  g,  g' ,  networks  of  lacteals. 

are    richly    supplied  with    networks    of    blood-vessels   and 
lymphatics.     Scattered  very  generally  along  the  intestine  in 


286  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  submucous  coat  are  nodules  of  lymphatic  tissue  which 
are  called  the  patches  of  Peyer.  These  patches  may  be  but 
tiny  nodules  invisible  to  the  unaided  eye,  or  may  attain  the 
size  of  lumps  distinctly  visible  and  easily  felt.  Such  larger 
patches  may  materially  distend  the  submucous  coat  and 
may  even  reach  up  into  the  mucous  coat  displacing  the  villi 
in  the  manner  indicated  in  Figure  115.  That  such  lymphatic 
glands  are  scattered  so  generally  through  the  wall  of  the 
small  intestine,  and  even  occur  in  numbers  in  the  mesent- 
ery, suggests  that  the  leucocytes  which  arise  in  these  glands 
may  in  some  direct  way  be  concerned  with  the  phenomena 
of  absorption. 

6.     THE  LARGE  INTESTINE. 

The  small  intestine  leads  into  the  large  intestine.  At 
the  point  of  the  junction  there  is  a  valve  called  the  ilio- 
colic  valve,  so  arranged  that  food  may  easily  pass  into  the 
large  intestine  but  cannot  pass  in  the  reverse  direction. 
The  opening  of  the  small  intestine  into  the  large  is,  how- 
ever, not  a  terminal  one,  the  ilio-colic  valve  being  situated 
on  the  side  of  the  large  intestine.  That  portion  which  is 
back  of  this  valve  is  spoken  of  as  the  blind  sac  or  the 
cczcum.  Attached  to  the  caecum  there  is  a  small  hollow 
continuation  known  as  the  vermiform  appendix.  While 
both  the  caecum  and  vermiform  appendix  in  man  are  quite 
small  and  probably  have  no  function  at  all  as  far  as  we 
know,  these  structures  are  very  large  in  the  herbivorous 
animals,  and  in  them  serve  to  hold  the  food  in  order  to  sub- 
ject it  more  thoroughly  to  the  digestive  action  of  the  juices 
and  the  absorptive  action  of  the  intestine. 

The  large  intestine  differs  materially  from  the  small  not 
only  in  its  larger  size,  but  also  in  its  structure.  The  mus- 
cular coats  are  not  so  well  developed,  the  circular  coat  in 
places  being  entirely  absent.  This  arrangement  of  the  cir- 
cular coat  gives  the  wall  of  the  large  intestine  its  pouched 
appearance.  On  the  mucous  coat  there  are  no  villi  at  all. 
The  crypts  of  L,ieberkuhn  of  the  small  intestine  are  here 
replaced  by  quite  similar  tubular  glands  which,  however, 


DIGESTIVE   ORGANS   AND    THEIR   ANATOMY. 


287 


do  not  produce  a  special  intestinal  juice,  but  secrete  mucus 
only.    They  are-,  therefore,  spoken  of  as  the  mucous  glands 


Fig.  116.— GLANDS  OF  THE  LARGE  INTESTINE.    (After  Heidenhain  and  Klose.j 
6,  longitudinal  section ;  c,  transverse  section ;  both  showing  mucous  secreting  goblet 

cells. 

of  the  large  intestine.  Except  that  they  are  a  little  larger 
and  that  they  contain  numerous  mucus-secreting  goblet 
cells,  they  are  analogous  to  the  crypts  of  the  small  intes- 
tine. The  mucous  secretion  of  these  glands  serves  to  lubri- 
cate the  walls  of  the  large  intestine  and  so  renders  more 
easy  the  translation  of  the  foods.  The  large  intestine  is 
much  shorter  than  the  small,  consisting  of  three  turns  only: 
an  upward  turn  on  the  right  side  of  the  body,  known  as  the 
ascending  colon,  a  turn  running  horizontally  across  the 
abdominal  cavity  just  beneath  the  stomach,  known  as  the 


288  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

transverse  colon,  and  a  descending  section  on  the  left  side 
known  as  the  descending  colon,  which  then  finally  through 
the  rectum  communicates  with  the  exterior. 

7.     THE  PANCREAS. 

The  pancreas  is  a  long,  slender  gland  of  reddish  yellow 
color  and  lies  immediately  below  and  back  of  the  stomach 
in  the  first  fold  of  the  duodenum.  It  is  about  five  or  six 
inches  long  and  from  three-quarters  to  an  inch  in  thickness. 
In  structure  this  gland  resembles  very  closely  the  salivary 
glands,  being  of  the  compound  racemose  type.  The  secret- 
ing cells  have  the  characteristic  glandular  appearance  and 
are  so  large  as  to  practically  fill  the  lumen  of  the  tubes. 
Examined  under  the  microscope  the  cells  at  rest  may  be 
seen  to  be  more  or  less  filled  with  trypsinogen  granules, 
while  when  examined  after  a  period  of  activity  the  cells 
seem  clear.  In  both  cases,  however,  the  lumen  of  the  tube 
is  exceedingly  small.  A  large  duct  runs  from  one  end  of 
the  gland  to  the  other  and  collects  all  of  the  pancreatic 
juice,  carrying  it  to  the  duodenum.  This  central  duct 
may  be  easily  seen  with  the  unaided  eye  as  a  whitish  tube, 
receiving  along  its  course  innumerable  smaller  branches 
from  the  tubules  which  it  passes,  and  finally,  in  conjunc- 
tion with  the  bile-duct  from  the  liver  flows  at  an  oblique 
angle  through  the  muscular  wall  of  the  intestine  and  pours 
its  secretion  into  that  organ.  This  duct  is  called  the  pan- 
creatic duct,  or  the  duct  of  Wirsung.  Sometimes  an  acces- 
sory duct  is  given  off  which  opens  into  the  duodenum  about 
an  inch  or  more  above  the  main  pancreatic  duct.  Indeed, 
in  some  instances  this  accessory  duct  may  become  larger 
than  the  main  duct.  This  accessory  duct  is  called  the  duct 
of  Santorini.  The  pancreas  is  richly  supplied  with  blood- 
vessels from  the  coeliac  axis,  and  lymphatics  and  nerves 
may  be  easily  traced  to  it.  On  account  of  its  action  on 
starches  the  pancreas  is  called  by  the  Germans  the  "ab- 
dominal salivary  gland."  Not  infrequently  it  is  referred  to 
by  our  butchers  as  the  abdominal  sweetbread,  in  this  case 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY.  289 

not  to  be  confounded  with  the  regular  sweetbread  of  the 
neck,  th,e  thymus  gland. 

8.     THE  LIVEE. 

By  far  the  largest  gland  in  the  body  is  the  liver.  It  has 
the  irregular  shape  familiar  to  all,  as  it  is  displayed  at 
the  meat  market.  The  human  liver  is  divided  into  two 
main  lobes,  a  larger  right  lobe  and  a  smaller  left  lobe, 
separated  more  or  less  by  the  round  ligament  of  the  liver 
which  is  the  remnant  of  a  blood-vessel  of  embryonic  life.  It 
measures  on  an  average  from  five  to  seven  inches  in  its 
greatest  vertical  extent,  and  its  greatest  transverse  diameter 
is  about  the  same.  In  bulk  the  liver  occupies  about  100 
cubic  inches  and  weighs  from  three  and  one-half  to  four 
and  one -half  pounds.  It  is  thus  about  -gV  to  iV  of  the 
weight  of  the  whole  body.  In  foetal  life  it  is  proportion- 
ately, however,  much  heavier,  being  at  birth  sometimes  as 
much  as  iV  of  the  entire  bodily  weight.  It  has  a  character- 
istic dull  reddish  brown  color.  The  ease  with  which  it 
may  be  cut  or  torn  is  readily  exemplified  on  the  butcher's 


Fig.  117.— CROSS-SECTION  OF  A  PORTAL  CANAL.     (Capsule  of  Glisson.) 
v,  portal  vein;    d,  bile-duct;    o,  hepatic  artery;   I,  lymphatic;   6,  blood-vessel  in  the 
tissue  of  the  canal  itself. 

counter.    It  is  covered  over  with  peritoneum,  but  has  in  ad- 
dition a  covering  of  its  own  called  the  capsiile  of   Glisson. 
19 


290 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


This  is  a  capsule  of  connective  tissue  which  extends  entirely 
over  the  liver,  but  which  underneath  extends  in  the  form  of 
solid  branched  trabeculse  up  into  the  gland  and  forms  the 
framework  of  its  inner  structure .  The  point  underneath  where 
this  capsule  of  Glisson  enters  the  liver  is  called  the  portal 
fissure.  These  trabeculae  of  connective  tissue  are  here  rami- 
fied through  the  interior,  carrying  in  their  ramifications 
branches  of  the  portal  vein,  the  hepatic  artery  and  the  bile- 
duct.  If  one  should  imagine  a  much-branched  elm  tree 
covered  with  heavy  canvas,  and  this  canvas  folded  around 
the  main  stem  near  the  ground,  and  made,  so  to  speak, 
continuous  with  it,  he  would  have  an  analogy  to  the  struc- 
ture of  the  liver,  the  canvas  representing  the  capsule  of 
Glisson  covering  the  entire  gland,  but  at  the  portal  fissure 
connected  with  a  system  of  ramifications  extending  through- 
out the  entire  gland.  If,  now,  we  should  imagine  passing 
through  the  stem,  and  through  every  branch  of  this  tree, 
even  down  to  the  finest  twigs,  three  tubes  running  side  by 


Fig.  118.— LONGITUDINAL  SECTION  OF  A  PORTAL  CANAL  CONTAINING  A  PORTAL  VEIN 

P.  P.;    TO   THE   RIGHT  AND   NEXT   TO  THE  VEIN  THE   SMALLER  BILE-DUCT;    AND   NEXT 
TO   THIS   THE   STILL    SMALLER   HEPATIC  ARTERY.      THE   INDIVIDUAL   LOBULES  OF  THE 

LIVER  ARE  PLAINLY  SHOWN.     (After  Kieruau.) 

side,  the  analogy  would  be  still  more  helpful.     These  tra- 
beculse which  run  upward  from  the  capsule  of  Glisson  carry 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY.  291 

the  same  name,  so  that  we  speak  of  the  capsule  of  Glisson 
in  the  liver  containing  the  three  ducts  just  mentioned. 
These  ramifications  finally  surround  the  real  units  of  the 
liver  structure,  which  are  the  hepatic  lobules.  These  lob- 
ules are  spherical,  or  on  account  of  being  pressed  by  jux- 
taposition, polyhedral  masses.  They  are  visible  to  the 
naked  eye,  giving  to  the  liver  that  marked-off  appearance 
readily  discernible  on  a  fresh  specimen,  and  accounting  for 
the  granular  feeling  when  fried  liver  is  masticated  or  rolled 
between  the  teeth.  The  lobules  are  made  up  of  innumerable 
hepatic  cells,  arranged  mote  or  less  in  rows,  radiating  from 
the  center  of  each  lobule  outward.  Around  and  between 
these  lobules  the  final  ramifications,  of  portal  vein,  hepatic 
artery  and  bile  duct  run.  These  end  branches  are  called 
respectively  the  interlobular  portal  vein,  the  interlobular 
hepatic  artery  and  the  interlobular  bile-duct. 

From  the  plexus  of  the  interlobular  portal  vein  capil- 
laries arise  which  run  into  the  lobule  from  all  directions  in 
such  a  way  as  to  meet  in  the  center.  This  capillary  net- 
work pervading  each  lobule  is  called  the  lobtilar  plexiis. 
While  this  lobular  plexus  is  formed  mainly  from  capillaries 
arising  from  the  portal  vein,  there  seems  little  doubt  but 
that  into  this  same  lobular  plexus,  blood  from  the  interlob- 
ular hepatic  arteries  is  poured.  We  have  here  then  a  con- 
dition of  things  in  which  a  single  capillary  plexus  is  fed  by 
two  streams — a  portal  vein  and  a  hepatic  artery.  The 
question  naturally  arises,  why  this  mixing  of  the  blood  from 
the  portal  vein  and  hepatic  artery  might  not  have  occurred 
before  entering  the  liver  at  all,  doing  away  with  a  double 
system  of  vessels  ramifying  throughout  the  substance  of  the 
liver.  The  explanation  is  found  in  the  fact  that  the  hepatic 
artery  is  used  mainly  to  carry  nutritious  blood  to  the  various 
ducts  in  connection  with  the  liver,  and  to  the  connective 
tissue  everywhere  pervading  it,  and  that  its  primary  func- 
tion is  not  to  carry  blood  to  the  liver  cells  themselves.  It 
seems,  however,  very  improbable  indeed  from  the  size  of 
the  hepatic  artery,  that  all  the  blood  passing  through  it 


292  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

should  be  used  in  merely   nourishing  inactive   ducts   and 
passive  connective  tissue,  and  it  is  therefore  quite  probable 


Fig.  119.— DIAGRAMMATIC  REPRESENTATION  OF  TWO  HEPATIC  LOBULES.    (After  Schafer.) 
P,  interlobular  branches  of  portal  vein ;  h,  intralobular  vein ;  S,  sublobular  vein ;  the 
lobular  plexus  of  capillaries  is  plainly  shown. 

that  much  of  the  blood  of  the  hepatic  artery  is  mixed  with 
the  blood  from  the  portal  vein  in  the  lobular  capillaries  of 
each  lobule. 

After  the  mixed  blood  passes  through  the  lobular  plexus 
it  is  collected  in  the  center  of  each  plexus  in  a  small  vein 
called  the  intralobular  vein,  a  word  signifying,  of  course, 
the  vein  within,  and  not  between  the  lobules.  The  intra- 
lobular veins  carry  the  blood  out  of  the  lobules,  and  uniting 
with  the  intralobular  veins  of  neighboring  lobules  form  the 
siib-lobular  veins,  which,  by  uniting  with  other  similar 
veins  finally  form  the  hepatic  veins  which  carry  the  blood 
just  passed  through  the  liver  in  the  manner  described  into 
the  vena  cava.  The  hepatic  veins  are  usually  several  in 
number,  and  as  the  vena  cava  runs  apparently  right  through 
the  liver  they  are  very  short  indeed,  and  are  nothing  more 
than  veins  in  the  liver  substance  itself.  The  interlobular 
bile-ducts  also  send  capillary  projections  into  each  lobule, 
which,  however,  do  not  meet  in  the  center,  each  capillary 
duct  ending,  or  more  properly  speaking,  beginning,  blind 


DIGESTIVE:  ORGANS  AND  THEIR  ANATOMY.          293 

near  the  middle  of  the  lobule.  These  capillary  ducts  run 
in-between  the  liver  cells,  and  into  them  is  poured  the  se- 
cretion of  the  bile,  which  then  through  the  complicated 
system  of  bile-ducts  is  finally  carried  to  the  intestine. 

In  order  to  store  the  secretion  of  the  liver,  so  that 
larger  quantities  may  be  available  when  they  are  needed, 
the  bile-duct  is  connected  by  means  of  a  cystic  duct  with 
the  gall-bladder,  a  small  muscular  pouch  several  inches  in 
diameter,  lying  under  the  liver.  The  bile  reaches  this  gall- 
bladder by  being  prevented  from  reaching  the  intestine,  the 
duct  leading  to  the  intestine  being  closed  by  sphincter  mus- 
cles, and  thus  forcing  the  bile  up  into  the  gall-bladder. 
From  time  to  time  these  sphincter  muscles  relax,  and  with 
a  simultaneous  contraction  of  the  gall-bladder  the  bile  is  ex- 
pelled in  spurts  into  the  duodenum.  That  portion  of  the 
duct  which  leads  from  the  liver  to  where  the  duct  from  the 
bladder  meets  it  is  called  the  hepatic  duct.  The  duct  lead- 
ing to  the  bladder  is  called  the  cystic  duct,  while  that  part 
of  the  duct  formed  by  the  union  of  the  two  and  which  con- 
nects with  the  duodenum  is  called  the  common  bile-duct 
(ductus  choledochus) .  As  stated  before,  this  duct  opens 
with  the  pancreatic  duct. 

The  liver  is  supplied  with  lymphatics,  running  mainly 
in  the  capsule  of  Glisson.  Nerves  reach  it  from  the  left 
pneumogastric  and  from  the  sympathetic  through  the  solar 
plexus  of  the  mesentery.  Like  the  blood-vessels,  these 
lymphatics  and  nerves  enter  the  liver  at  the  portal  fissure. 

THE  DUCTLESS  GLANDS. 

The  various  structures  so  far  described  in  this  chaptei 
are  structures  intimately  and  integrally  connected  with  the 
process  of  digestion.  There  are,  however,  found  along  the 
alimentary  canal,  though  not  immediately  connected  with 
it,  other  organs  commonly  designated  as  the  ductless  glands. 
While  it  is  probable,  in  fact  known,  that  the  function  of 
some  of  these  glands  is  not  related  immediately  to  the  pro- 
cess of  digestion,  yet  it  is  customary,  on  account  of  their 


294 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


position,  possibly,  to  treat  them  in  connection  with  the  di- 
gestive tract.  This  is  at  least  allowable,  since  the  func- 
tion of  several  of  these  structures  is  practically  not  at  all 
understood,  and  so  could  not  be  scientifically  treated  any 
better  in  connection  with  other  topics.  These  ductless 
glands  include  the  thyroid  glands,  the  thymus  gland,  the 
spleen,  the  adrenal  bodies,  scattered  lymphatic  glands,  the 
carotid  glands,  and  the  coccygeal  gland. 

1. — The  thyroid  glands.  The  thyroid  glands  are  two 
large  dark  reddish,  vascular  structures  situated  in  the  neck 
just  below  and  to  the  side  of  the  voice-box.  The  two  lobes 
are  usually  connected  with  a  transverse  portion  called  the 
isthmus.  It  varies  in  length,  each  lobe  measuring  an  inch 
to  an  inch  and  a  half,  while  the  thickest  portion  is  about 
an  inch.  The  isthmus  connecting  these  two  lobes  is  about 
one-half  an  inch  wide  and  about  three-quarters  of  an  inch 
long.  Examined  roughly  the  structure  of  the  organ  seems 
to  be  granular.  This  is  borne  out  by  a  microscopic  examin- 


Fig.  120.— SHOWING  THE  RELATIVE  POSITIONS  AND  SIZES  OF  THE  THYMUS  AND  THYROID 

GLANDS  IN  A  CHILD.     (After  Sappey.) 

1,2,3,4,  thymus  gland;   6,  thyroid  gland,  covered  with  a  number  of  blood-vessels. 
All  the  other  numbers  refer  to  blood-vessels. 

ation  of  the  gland,  which  shows  that  it  is  composed  of  in- 
numerable vesicles  which  are  bound  together  more  or  less 
firmly  by  intervening  areolar  tissue.  Each  vesicle  is  usu- 
ally quite  small,  at  best  just  visible  to  the  unaided  eye. 


DIGESTIVE   ORGANS   AND   THEIR   ANATOMY.  295 

However,  in  certain  diseases  of  the  thyroid  glands,  such  as 
goitre,  these  vesicles  may  become  greatly  distended  and 
plainly  discernible  to  the  naked  eye. 

The  wall  of  these  vesicles  is  made  up  of  a  single-layered 
epithelium,  in  which  the  individual  cells  are  somewhat  cub- 
ical or  columnar.  In  the  interior  there  is  found  a  yellowish 
fluid,  which  is  no  doubt  the  material  secreted  by  these  epi- 
thelial cells.  This  same  fluid  also  occurs  in  the  areolar  tissue 
between  the  vesicles.  This  fluid  on  account  of  its  appearance 
is  spoken  of  as  a  colloid  substance.  In  certain  forms  of  goitre 
this  colloid  substance  accumulates  to  such  an  enormous  ex- 
tent as  to  increase  the  size  of  the  gland  to  many  times  its  orig- 
inal dimensions.  The  connective  tissue  between  the  vesicles 
is  richly  supplied  with  blood-vessels  and  lymphatics,  which 
seems  to  indicate  the  important  part  which  this  gland  plays 


Fig.  121.— SECTION  OF  A  HUMAN  THYROID  GLAND.    (After  Schafer.) 
Two  complete  vesicles  and  portions  of  three  others  are  shown.    The  colloid  material 
filling  both  the  vesicles  and  the  spaces  between  is  indicated.    In  the  center  of  figure  is  a 
blood-vessel  cut  across,  next  to  this  a  plasma  cell. 

in  the  economy  of  the  body.  The  composition  of  this  col- 
loid material  has  not  been  satisfactorily  determined.  By  some 
observers  it  is  stated  that  it  contains  proportionately  large 
amounts  of  phosphorus.  More  recent  experiments  have 
shown  that  besides  containing  substances  of  an  albuminous 
or  proteid  nature  it  contains  a  compound  of  iodine  called 
thyro-iodine. 


296  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

Function. — The  function  of  this  gland  has  not  been  made 
satisfactorily  clear.  When  the  gland  is  removed  from  the 
body  peculiar  pathological  symptoms  result,  associated  with 
mental  disturbances  which  finally  result  in  insanity  and  death. 
It  has  therefore  been  supposed  by  some  physiologists  that 
this  gland  normally  removes  from  the  body  a  kind  of  poison 
which,  when  it  accumulates,  causes  all  these  pathological 
symptoms.  Such  physiologists  would  look  upon  the  thyroid 
body  as  an  anti-toxine  agent.  In  fact,  certain  observers 
have  tried  to  establish  that  in  animals  deprived  of  the  thy- 
roid body  there  was  actually  an  accumulation  of  poisons  in 
the  blood  to  such  an  extent  that  when  this  blood  was  in- 
jected into  other  animals  it  poisoned  them.  The  difficulty 
of  taking  into  consideration  all  possible  errors  in  such  an 
experiment  makes  it  impossible  to  rely  with  assurance  up- 
on its  results,  and  more  recently  physiologists  have  gone  to 
the  view  that  the  thyroid  glands  do  not  remove  a  substance 
from  the  body  which  is  injurious,  but  produce  a  substance 
for  the  body  which  is  not  only  beneficial  but  indispensable. 
Experiments  have  been  made  by  injecting  extracts  of  the 
thyroid  gland  into  animals,  the  result  being  a  beneficial 
quickening  of  the  general  body  metabolism.  Physiologists 
holding  this  view  would  explain  the  pathological  symptoms 
which  follow  the  loss  of  these  glands,  such  as  the  diminu- 
tion of  muscular  strength,  failure  of  the  mental  powers, 
swelling  of  the  connective  tissues,  and  excessive  dry  ness  of 
the  skin,  as  a  result  of  the  absence  of  this  necessary  tonic 
secreted  in  the  thyroids,  and  it  ought  therefore  to  follow,  if 
this  view  is  correct,  that  the  administration  of  an  extract  of 
the  thyroid  gland  ought  to"  produce  the  normal  condition.  It 
is  a  remarkable  fact  that  in  human  beings  suffering  from 
such  symptoms  as  the  result  of  the  loss  of  the  function  of 
the  thyroid,  injections  of  thyroid  extract,  or  even  feeding 
them  some  fresh  gland  soon  restores  the  individual  to  a 
practically  normal  condition. 

It  is  unfortunate,  from  a  physiological  point  of  view, 
that  a  gland  which  seems  to  play  such  an  important  role  in 


DIGESTIVE   ORGANS   AND    THEIR   ANATOMY.  297 

the  life  of  the  body  and  which  is  so  indispensable  to  its  ex- 
istence, should  be  so  poorly  understood.  Investigators  have 
not,  however,  abandoned  the  research,  and  it  is  possible 
that  the  development  of  the  next  few  years  may  throw  hope- 
ful light  on  this  subject.* 

1  Sometimes  there  are  found  in  the  immediate  neighbor- 
hood of  the  thyroids  small  nodules  of  similar  tissue  which 
are  called  para-thyroids.  These  are  no  doubt  identical  with 
the  regular  thyroid  glands  in  structure  and  function.  When 
in  certain  animals  the  removal  of  the  main  thyroid  does  not 
produce  immediate  death,  these  para- thyroids  may  be,  no 
doubt,  under  such  circumstances  fulfilling  the  same  function. 

2. — The  Spleen.     Lying    on  the  left  side  of  the  body 
in  a  position  corresponding  somewhat  to  the  liver  on  the 


*  With  the  permission  of  Dr.  Robert  Hessler,  the  Pathologist  of  the  Central  Indiana 
Hospital  for  Insane,  at  Indianapolis,  extracts  from  a  recent  clinical  report  of  his  are 
here  added.  These  extracts  are  reports  of  cases  of  Thyroid  Medication. 

CASE)  I. — This  is  the  case  mentioned  in  my  former  paper;  a  young  man  who  had 
lain  immovable  in  bed  for  over  three  years,  and  who  could  not  be  aroused  by  any  means; 
was  fed  twice  a  day  by  means  of  a  stomach-tube.  Under  constantly  increasing  doses  of 
thyroid  gland  he  gradually  returned  to  life,  but  showed  a  tendency  to  relapse  on  with- 
holding the  remedy.  Under  very  large  doses  symptoms  of  exopthalmic  goitre  appeared. 
He  has  received  thyroids  since  November  1,  1895,  and  still  requires  moderate  daily  doses 
to  enable  him  to  move  about.  He  is  in  the  best  ward  in  the  hospital,  goes  out  to  his 
meals,  and  takes  walks  about  the  grounds.  Mentally  he  is  sluggish,  and  is  not  inclined 
to  exert  himself;  there  is  some  mental  impairment.  Whether  he  will  ever  fully  recover 
is  still  a  question. 

CASE)  II.— A  middle-aged  German,  cataleptic  for  three  years,  retained  for  a  long 
time  any  position  in  which  he  was  placed,  even  the  most  awkward.  He  promptly  re- 
sponded to  the  thyroid  treatment,  and  in  a  few  weeks  was  able  to  be  about,  and  the  rem- 
edy was  discontinued.  After  gaining  strength  and  regaining  the  use  of  his  extremities — 
he  had  been  practically  bedfast  for  three  years — he  for  several  months  assisted  the  florist 
in  all  sorts  of  work  about  the  grounds,  and  ultimately  returned  home  well  in  body  and  in 
mind.  He  remembered  the  condition  he  had  been  in,  and  fully  appreciated  what  had 
been  done  for  him.  A  long  account  which  he  wrote  about  himself,  on  recovering,  is 
worthy  a  psychologist's  study.  He  had  realized  more  or  less  fully  at  all  times  what  went 
on  about  him,  but  his  actions  were  dominated  by  delusions. 

CASE)  IV. — This  was  a  man  approaching  middle  age  who  had  been  in  the  hospital 
several  years  before,  in  a  cataleptic  condition,  but  since  nothing  could  be  done  for  him  at 
that  time,  his  relatives  had  taken  him  home.  He  was  re-admitted  to  the  hospital  early  in 
May,  18%,  in  a  stuporous  condition,  as  if  asleep ;  no  mental  reactions  could  be  obtained  with 
stimuli  of  any  kind.  Sensitiveness  to  painful  stimuli  greatly  diminished.  In  poor  bodily 
condition;  weight  88  pounds;  his  normal  weight  had  been  about  150.  Extremities 
wasted;  little  motion  of  them;  in  fact,  they  were  almost  anchylosed  from  non-use. 
Hands  and  fingers  contracted;  attempts  to  straighten  them  brought  on  symptoms  of  pain. 
After  a  few  days  of  observation  in  the  hospital  he  was  placed  on  desiccated  thyroids  in  in- 
creasing doses.  After  a  month's  treatment,  signs  of  awakening  appeared,  and  in  three 
months  there  was  some  activity,  both  bodily  and  mental.  Massage  was  actively  applied. 
At  the  end  of  September,  under  a  daily  dose  of  thirty-five  grains,  vomiting  and  diarrhoea 


298  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

right,  is  a  soft  dark  purplish  organ  called  the  spleen.  Its 
dark  purplish  color  at  once  enables  the  observer  to  distin- 
guish it  from  the  pancreas,  which  is  light  colored.  Popu- 
ularly  the  spleen  is  referred  to  as  the  "melt."  '  It  has  no 
ducts  leading  from  it  all.  It  is  supplied  from  the  aorta 
with  a  rather  large  splenic  artery  and  connected  with  the 
vena  cava  with  a  large  splenic  vein.  It  is  covered  over  with 
peritoneum,  but  in  addition  to  this  has  a  connective  tissue 
capsule  of  its  own.  This  capsule  is  largely  fibrous,  but  con- 
tains also  bands  of  plain  muscular  fibres,  to  the  presence  of 
which  the  contractions  and  dilatations  which  this  organ  un- 
dergoes may  be  referred.  From  this  fibrous  capsule  trabec- 
ulse  extend  in  through  the  gland  and  form  a  fine  network 
throughout  its  interior.  This  network  is,  of  course,  almost 


appeared— thyroidism— and  the  remedy  was  stopped  for  a  few  days  and  then  resumed 
under  a  decreased  dosage  of  ten  grains  a  day,  slowly  increased  in  the  course  of  time.  By 
November  he  was  able  to  sit  up  in  bed  and  made  attempts  to  use  his  extremities ;  the 
mental  condition  was  fair.  He  continued  to  improve  rapidly,  and  by  the  middle  of  Janu- 
ary, 1897,  he  was  able  to  rise  and  put  on  his  coat;  he  even  attempted  to  write  a  letter. 
During  March  thyroids  were  discontinued;  the  daily  dose  at  that  time  was  twenty-five 
grains.  The  patient  at  this  time  was  able  to  use  his  legs  to  some  extent,  and  by  the  mid- 
dle of  the  summer  he  was  able  to  walk  about  unassisted.  This  recovery  was  truly  re- 
markable. He  has  not  had  any  further  thyroid  medication  since  March.  Unfortunately, 
mental  improvement  did  not  keep  pace  with  the  bodily.  The  patient  had  been  a  mild 
maniac  years  ago,  and  symptoms  of  this  would  crop  out  now  and  then;  he  is,  therefore, 
still  detained  in  the  hospital. 

CASE)  XVI. — Age  thirty-three ;  recently  passed  the  acute  mania  stage  and  became 
chronic.  At  the  beginning  of  the  thyroid  treatment  he  was  quiet  and  well-behaved,  al- 
though delusional  and  wholly  irrational.  Under  the  influence  of  the  gland  he  became  more 
active;  marked  symptoms  of  acute  mania  reappeared;  the  heart  acted  powerfully,  and  the 
eyes  bulged  slightly.  Such  a  reaction  was,  of  course,  not  desired,  and  the  remedy  was 
stopped,  after  having  been  given  for  several  weeks.  He  soon  relapsed  to  his  former  quiet 
condition. 

Conclusions.— My  conclusions,  based  on  my  experience,  may  be  briefly  stated  about 
as  follows: 

Under  moderate  continued  doses  of  thyroid  gland  there  is  a  marked  bodily  reaction 
in  many  cases,  but  not  in  all.  Some  cases  require  comparatively  large  amounts  before 
any  reaction  occurs.  There  is  a  distinct  stimulation  of  the  nervous  system,  manifested 
in  various  ways,  and  all  bodily  activities  are  increased.  Tissue  metabolism,  especially  of 
the  muscular  and  nervous  systems,  is  markedly  increased;  a  considerable  loss  in  body 
weight  occurs  in  a  short  time;  on  suspending  the  remedy  a  rapid  gain  in  weight  usually 
follows.  In  some  cases  there  is  a  temporary  lighting  up  of  sensory  or  motor  activities, 
one  or  both,  which  soon  disappear  on  discontinuing  the  remedy.  Some  cases  of  a  certain 
type  (cataleptics)  are  benefited  permanently;  apparently  all  that  is  required  for  a  restor- 
ation to  a  life  of  normal  activity  is  the  stimulus  derived  from  the  substance  of  the  gland. 

In  moderate  doses  no  ill  results  are  produced.  Under  very  large  continued  doses 
a  reaction  occurs  which  is  essentially  an  artificial  attack  of  exopthalmic  goitre,  Any  un- 
favorable symptoms  appearing  under  large  dosage  promptly  disappear  on  withholding 
the  remedy. 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY.  299 

wholly  connective  tissue,  and  so  far  as  structure  is  con- 
cerned reminds  one  of  the  connective  tissue  of  lymphatic 
glands.  In  the  meshes  of  this  connective  tissue  is  the 
spleen  pulp.  This  is  loosely  contained  and  may,  when  the 
gland  is  cut,  be  more  or  less  completely  washed  out,  leav- 
ing the  framework  exposed.  When  the  spleen  is  cut  and 
this  pulp  forced  out  it  looks  very  much  like  clotted  blood, 
which  in  fact  it  mainly  is.  Such  pulp  examined  with  a 
microscope  is  seen  to  consist  of  ordinary  red  and  white 
blood  corpuscles,  the  latter  in  relatively  greater  number 
than  in  normal  blood.  Among  these  are  many  connective 
tissue  cells,  found  here,  no  doubt,  for  the  same  reason  that 
they  occur  in  all  the  connective  tissues.  Among  the  white 
blood  corpuscles,  however,  there  may  be  seen  now  and  then 
in  fresh  spleen  pulp  somewhat  larger  cells  exhibiting  to  a 
much  greater  extent  amoeboid  movements.  These  cells  not 
infrequently  have  in  them"  red  corpuscles  in  all  stages  of 
disintegration,  and  from  this  observation  physiologists  have 
naturally  come  to  the  belief  that  these  cells  in  the  spleen 
must  be  concerned  in  the  destruction  of  red  corpuscles. 
These  cells  are  called  the  splenic  cells. 

The  blood-vessels  of  the  spleen  are  peculiarly  interest- 
ing. The  artery  on  entering  the  spleen  divides  and  sub- 
divides, but  the  smaller  arteries  are  not  connected  with 
veins  by  means  of  capillaries  as  in  other  portions  of  the 
body,  but  the  arteries  open  abruptly,  right  into  the  spleen 
pulp,  thus  allowing  the  blood  to  soak  at  large  through  the 
interstices  of  the  gland.  On  the  other  hand  the  veins  orig- 
inate as  open  ducts  collecting  the  blood  which  has  soaked 
through  the  pulp.  At  the  ends  of  these  small  arteries,  that 
is,  just  where  they  open  abruptly  into  the  spleen  pulp  and 
to  a  somewhat  smaller  extent  at  the  beginning  of  the  veins, 
there  are  situated  little  nodules  of  lymphatic  tissue  not  un- 
like the  patches  of  Peyer  in  the  intestines.  These  may  be 
exceedingly  small,  or  may  reach  dimensions  so  as  to  be 
plainly  visible  as  whitish  specks  to  the  unaided  eye.  These 
aggregations  of  white  corpuscles  are  called  the  Malpighian 


300  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

corpuscles  of  the  spleen.     It  must  be  remembered,  however, 
that  the  word  '  *  corpuscles  ' '  is  here  not  used  in  its  usual 


Fig.  122.— VERTICAL  SECTION  OF  A  PORTION  OF  THE  HUMAN  SPLEEN.    (After  Kolliker.) 
a,  A,  fibrous  capsule;  6,  6,  fibrous  trabeculse  running  through  gland;  c,  c,  Malpighian 
corpuscles;  d,  d,  injected  arteries;  e,  the  spleen  pulp. 

sense,  that  it  does  not  refer  to  a  single  structure,  but  to 
an  aggregation  of  white  corpuscles  in  the  form  of  a  lym- 
phatic nodule.  In  this  sense  a  patch  of  Peyer  in  the  intes- 
tine might  be  called  a  Malpighian  corpuscle  of  the  intestine. 
Further,  these  Malpighian  corpuscles  must  not  be  confounded 
with  the  splenic  corpuscles  just  referred  to,  which  are  really 
true  corpuscles,  but  which  are  found  mainly  in  the  inter- 
stices between  the  Malpighian  corpuscles.  From  the  struc- 
ture of  the  spleen  it  will  be  noticed  that  it  is  essentially  a 
lymphatic  gland,  but  that  unlike  true  lymphatic  glands 
blood  and  not  lymph  traverses  it.  By  the  arrangement  of 
the  blood-vessels  the  blood  is  brought  into  close  contact 
with  the  cells  that  go  to  make  up  the  splenic  pulp,  and  it 
is  there  no  doubt  subjected  to  important  physiological  mod- 
ifications, which  unfortunately  are  not  sufficiently  under- 
stood. 

The  function  of  the  spleen  is  still  a  chapter- reserved  for 
future  investigation.   That  it  is  not  essential  to  life  is  proved 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY.  301 

by  the  fact  that  the  spleen  may  be  taken  out  of  an  animal 
without  in  any  serious  way  inconveniencing  it.  It  shows  a 
slight  connection  with  the  process  of  digestion  in  the  fact 
that  soon  after  a  meal  the  spleen  becomes  materially  larger, 
then  contracts  again  during  the  fasting  period.  In  addition 
to  these  meal  pulsations,  observers  have  noticed  that  it  un- 
dergoes at  all  times  slight  contractions  and  expansions. 
They  have  been  stated  by  some  to  be  at  the  rate  of  about 
one  expansion  per  minute.  These  secondary  expansions  are, 
however,  quite  slight,  and  may  be  due  to  slight  changes  in 
blood  pressure.  Various  functions  have  been  ascribed  to 
it.  It  has  been  supposed  that  red  corpuscles  were  formed 
here.  This  is  true  during  foetal  life  and  for  a  short  time 
after  birth,  but  there  is  really  no  evidence  at  all  for  the  view 
that  in  adult  life  red  corpuscles  are  formed  here.  Then,  on 
the  other  hand,  it  has  been  believed  by  many  to  be  a  place 
where  red  corpuscles  are  destroyed.  In  evidence  of  this 
fact  is  cited  the  observation  just  mentioned,  that  certain 
cells  of  the  spleen  frequently  have  in  their  interior  red  cor- 
puscles in  all  stages  of  disintegration.  A  further  fact  which 
helps  to  support  this  view  is  the  large  proportionate  amount 
of  iron  which  is  found  in  the  spleen,  and  it  has  been  be- 
lieved that  this  iron  comes  from  the  destruction  of  the  iron- 
containing-hsemoglobin  of  red  corpuscles.  While  there 
seems,  therefore,  at  present  much  probability  that  this  view 
is  the  correct  one,  it  is  not  yet  an  undisputed  fact.  The 
ability  to  produce  new  white  corpuscles  has  been  ascribed 
to  the  spleen.  This  is  no  doubt  true.  The  presence  of 
much  lymphatic  tissue  in  the  spleen  would  make  readily 
possible  the  formation  of  new  white  corpuscles  just  as  in  all 
other  lymphatic  tissue.  Recently  the  view  has  been  ad- 
vanced that  in  the  spleen  there  is  formed  a  kind  of  ferment 
which  when  it  reaches  the  pancreas  (through  the  blood) 
changes  the  trypsinogen  contained  in  this  gland  into  the 
trypsin.  There  is  so  little  evidence  to  support  this  view 
that  it  has  been  accepted  by  practically  no  physiologists  of 
any  note.  In  short,  w*e  may  say  of  the  function  of  the  spleen, 


302  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

first,  that  containing  much  lymphatic  tissue,  it  gives  rise  to 
white  corpuscles;  second,  that  the  splenic  pulp  is  no  doubt 
largely  instrumental  in  removing  from  the  blood  passing 
through  it  degenerate  red  corpuscles. 

The  fact  that  the  spleen  may  be  removed  without  seri- 
ous injury  to  an  animal  may  be  explained  on  the  ground 
that  there  are  many  lymphatic  glands  in  the  body  able  to 
produce  white  corpuscles,  and  that  the  destruction  of  the 
red  corpuscles  naturally  done  by  the  spleen  might  be  as- 
sumed by  the  liver,  in  which,  regularly,  a  wholesale  destruc- 
tion takes  place. 

3. — TJie  adrenal  bodies.  Situated  immediately  above 
each  kidney  there  is  a  small  glandular  mass  called  the  ad- 
renal body,  or  not  infrequently,  the  supra-renal  body.  The 
right  and  left  adrenals  do  not  have  the  same  form,  but  are 
about  the  same  in  bulk.  They  measure  from  one  to  two 
inches  from  above  downward,  and  from  about  one  inch 
to  an  inch  and  a  half  from  side  to  side.  Their  thickness  is 
only  about  one-fifth  of  an  inch.  From  these  dimensions  it 
will  be  seen  that  they  are  by  no  means  tiny  structures,  and 
from  their  size  and  the  richness  of  their  vascular  supply 
one  might  suspect  that  they  play  an  important  role  in  the 


Fig.  123.— SECTION  THROUGH  THE  SUPRA-RENAL  BODY.     (After  Allen  Thomson.) 
_      r,  kidney;   w,  supra-renal  vein;   the  distinction  between  cortex  and  medulla  is  also 
shown. 

body.    Each  adrenal  body  is  covered  with  a  capsule  of  con- 
nective tissue  through  which  is  visible  the  somewhat  yellow-  . 
ish  or  brownish  yellow  gland.    The  gland  itself  is  composed 


DIGESTIVE    ORGANS    AND    THEIR    ANATOMY.  303 

of  an  outer  cortical  region,  of  a  deep  yellow  color,  consisting 
of  rods  of  cells  and  an  inner  medullary  portion  of  a  more 
blackish  color  and  quite  soft  and  pulpy. 

A  closer  examination  of  this  gland  reveals  that  the  cor- 
tex consists  of  a  framework  of  connective  tissue,  in  which 
are  imbedded  column-like  groups  of  cells.  In  these  col- 
umns of  cells  there  is,  however,  no  lumen  visible,  so  that 
they  are  evidently  not  like  the  tubular  glands  found  else- 
where. The  medullary  portion  consists  of  a  much  looser 
framework  of  connective  tissue,  richly  supplied  with  capil- 
laries, while  distributed  through  the  interstices  of  this 
framework  there  are  groups  of  cells  which  resemble  some- 
what those  found  in  the  cortex.  The  function  of  these 
structures,  like  that  of  the  thyroid  and  spleen,  is  still  in 
doubt.  The  removal  of  these  bodies  is  rapidly  followed  by 
death.  The  symptoms  which  follow  such  removal  are  great 
muscular  weakness  and  relaxation  of  most  of  the  blood-ves- 
sels, and  a  general  prostration.  Similar  symptoms  occur 
in  a  disease  in  man  known  as  Addison's  disease,  which 
clinical  evidence  has  referred  to  pathological  conditions  of 
the  adrenal  bodies.  This  disease  is  especially  marked  by 
the  appearance  of  bronzed  patches  on  the  skin,  and  so  the 
view  has  arisen  that  possibly  these  supra-renal  bodies  are 
concerned  in  the  elimination  of  an  injurious  pigment  from 
the  blood,  which,  when  it  accumulates,  produces  the  gen- 
eral poisonous  effects,  and  finally,  if  sufficiently  concentrated, 
discolors  the  skin  to  a  deep  bronze.  On  the  other  hand, 
some  observations  seem  to  indicate  that  this  gland  does  not 
remove  an  injurious  pigment  from  the  blood,  but  that  it 
adds  some  beneficial  substance  which,  when  removed,  leads 
to  the  described  results.  Aqueous  extracts  of  the  adrenal 
bodies  have  been  made  and  injected  into  the  blood-vessels 
of  living  animals  with  the  result  that  it  affected  in  a  remark- 
able way  the  action  of  the  heart,  the  blood-vessels,  and  even 
the  voluntary  muscles.  It  made  the  contractions  of  the 
heart  more  prolonged,  strongly  contracted  the  blood-vessels, 
and  so  produced  a  great  increase  in  blood  pressure  and  pro- 


304  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

longed  the  contractions  of  the  voluntary  muscles.  The  ef- 
fects of  such  an  injection  are  soon  worn  off,  showing  that 
the  active  principle  of  the  extract  is  soon  destroyed  or 
eliminated  from  the  body.  It  will  be  seen,  however,  that 
at  best  our  knowledge  is  in  a  most  unsatisfactory  state,  and 
while  it  is  possible  that  these  adrenals  may  be  concerned  in 
forming  some  kind  of  tonic  substance  which  proves  bene- 
ficial and  indispensable  to  the  proper  working  of  other  tis- 
sues, it  seems  more  probable  that  it  is  concerned  with  the 
removal  of  injurious  substances  already  present  in  the 
blood.  This  latter  view  is  materially  strengthened  by  the 
observation  that  Addison's  disease,  marked  especially  by 
accumulation  of  such  pigment,  follows  abnormal  conditions 
of  these  adrenal  bodies. 

4. — The  Thymus  Gland.  The  thymus  gland  is  a  tem- 
porary structure  which  is  quite  large  in  early  life,  reaching 
its  maximum  size  about  the  second  or  third  year  of  life,  and 
then  gradually  dwindling  away  until  adult  life,  when  it  is 
practically  gone.  It  is  situated  in  the  lower  region  of  the 
neck  and  the  upper  part  of  the  chest,  and  when  at  its  max- 
imum development  is  quite  large.  Its  dimensions  about 
the  time  of  birth  are  two  inches  in  length  and  about  one 
and  a  half  inches  in  width,  with  a  thickness  of  about  one- 


Fig.  124.— PART  OF  THE  MEDULLA  OF  A  THYMUS  GLAND,  SHOWING  SEVERAL  OF  THE 

RETICULAR   FIBRES,  A   NUMBER   OF   LYMPHOID   CELLS  CALLED  THYMUS  CORPUSCLES,  a; 

AND  TWO  CONCENTRIC  CORPUSCLES,  6.     (After  Cadiat.) 

third  of  an  inch.  In  some  of  the  lower  animals  this  gland 
may  reach  rather  remarkable  dimensions.  In  a  calf  it  may 
be  as  much  as  six  or  eight  inches  in  length  and  two  or 


DIGESTIVE    ORGANS   AND    THEIR   ANATOMY.  305 

three  inches  in  width.  The  gland  figures  in  the  business 
of  the  meat  dealer,  and  is  sold  under  the  name  of  sweet- 
breads. 

The  thymus  is  made  up  of  two  lobes  of  almost  the  same 
size,  which  lobes,  however,  usually  lie  close  together,  meet- 
ing each  other  at  their  inner  surfaces.  In  structure  the 
thymus  gland  is  a  typical  lymphatic  gland.  It  is  invested 
with  a  capsule  of  fibrous  connective  tissue,  from  which 
trabeculse  extend  into  the  gland,  subdividing  it  and  form- 
ing a  framework  throughout  its  interior.  In  the  meshes  of 
this  framework  are  imbedded  innumerable  white  corpuscles. 
The  trabeculae  extending  in  from  the  capsule  divide  the  in- 
terior off  into  little  chambers  or  lobules  in  which  the  cor- 
puscles show  an  arrangement  in  two  layers,  an  outer  layer 
of  ordinary  white  corpuscles  closely  packed,  and  similar  in 
every  way  to  lymphoid  structure  wherever  found.  The 
fact  that  these  cells  are  spoken  of  as  the  thymus  corpuscles 
must  not  lead  to  the  idea  that  they  are  in  any  way  different 
from  ordinary  lymphoid  corpuscles.  In  the  center  of  each 
lobule  the  corpuscles  are  not  arranged  so  closely,  and  there 
are  found  here  and  there  imbedded  among  the  ordinary  cor- 
puscles nests  of  cells  which  show  a  concentric  structure. 
These  are  called  the  concentric  corpuscles  of  Hassall. 
Each  nest  seems  to  be  composed  of  a  covering  of  hardened 
epithelium  cells  enclosing  one  or  more  granular  cells. 
While  the  meaning  of  these  concentric  corpuscles  is  not 
wholly  clear,  there  is  much  reason  to  believe  that  they  are 
but  remains  of  a  primitive  epithelial  tube  which  occurs  in  a 
developing  thymus  and  so  have  no  physiological  signifi- 
cance. 

From  its  structure  it  would  seem,  then,  that  the  thymus 
gland  is  but  a  gigantic  lymphatic  nodule  and  as  such  is  con- 
cerned in  the  production  of  new  white  corpuscles.  That  it 
disappears  in  advancing  life  may  be  easily  accounted  for  by 
the  fact  that  new  lymphatic  nodules  appear  in  many  other 
parts  of  the  body  which  may  relieve  the  thymus  from  the 
necessity  of  further  use.  That  the  thymus  reaches  such  a 
20 


306  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

relatively  large  size  in  early  life  would  indicate  that  either 
lymphatic  tissue  has  not  appeared  abundantly  in  other  parts 
of  the  body,  or  that  in  the  growing  organism  there  is  an 
especially  great  demand  for  new  cells.  Unlike,  however, 
ordinary  lymphatic  glands,  the  thymus  seems  richly  sup- 
plied with  blood-vessels.  Fine  vessels  penetrate  to  the  in- 
dividual follicles,  forming  a  plexus  around  them  and  send- 
ing converging  capillaries  into  the  medullary  portion.  The 
lymphatics  which  transverse  the  interstices  of  the  gland  are 
very  large.  It  is  poorly  supplied  with  nerves,  although  a 
few  filaments  derived  from  the  pneumogastric  and  the  sym- 
pathetic system  reach  the  gland  by  way  of  its  arteries. 

5. — The  Carotid  Glands.  Situated  just  above  the  point 
at  which  the  common  carotid  artery  on  each  side  divides 
into  an  internal  and  external  branch  there  is  a  small  gland- 
ular nodule  called  the  carotid  gland.  It  has  a  connective 
tissue  capsule,  trabeculse  from  which  extend  into  the  in- 
terior, dividing  it  into  small  lobules.  These  lobules  are 
composed  of  masses  of  epithelium-like  cells,  around  and  be- 
tween which  there  are  distributed  numerous  blood  capillaries. 
Their  physiological  importance  may  be  dismissed  by  saying 
that  we  have  absolutely  no  knowledge  as  to  what  their  func- 
tion is. 

6. — The  Coccygeal  Gland.  The  coccygeal  gland  is  a 
small  glandular  nodule  only  two  or  three  millimeters  in 
diameter,  situated  at  the  apex  of  the  coccyx.  It  does  not 
differ  materially  in  structure  from  the  carotid  glands,  being 
composed  of  masses  of  epithelium-like  cells  surrounded  with 
blood  capillaries.  Concerning  this  gland  we  are  also  com- 
pletely in  the  dark,  both  as  to  the  manner  in  which  it  de- 
velops and  as  to  its  function. 

7. — The  Pituitary  Body.  Situated  at  the  end  of  the  in- 
fundibulum  of  the  brain  (which  see)  there  is  a  small  glandu- 
lar nodule  about  the  size  of  a  small  pea  known  as  the 
pituitary  body.  It  is  enclosed  in  a  special  prolongation  of 
the  dura  mater  and  is  composed  of  two  lobes.  In  color  it 


DIGESTIVE    ORGANS    AND    THEIR   ANATOMY.  307 

is  of  a  reddish  gray  appearance.  It  owes  its  name  to  the 
belief  of  the  ancients  that  it  discharged  the  Clpituita" 
(phlegm)  into  the  nostrils.  In  structure  it  consists  of  con- 
nective tissue,  in  which  there  are  imbedded  numerous 
branched  cells. 

There  is  possibly  no  reason  for  treating  of  this  structure 
in  connection  with  the  organs  concerned  in  digestion,  or 
even  in  connection  with  the  ductless  glands,  except  for  the 
fact  that  experiments  seem  to  indicate  that  its  function  is 
closely  allied  to  that  of  the  thyroid  glands.  Complete  re- 
moval of  the  pituitary  body  causes  immediate  death.  Death 
is  preceded  by  symptoms  such  as  general  prostration  and 
spasms,  and  mental  weakness,  which  are  quite  similar  to 
those  following  the  removal  of  the  thyroids.  This  has  led 
many  observers  to  believe  that  physiologically  the  pituitary 
body  is  a  thyroid,  and  is  able  to  assume  to  some  extent  at 
least,  the  functions  of  these  glands.  However,  the  con- 
dition of  our  knowledge  is  best  stated  by  saying  that  with 
the  exception  of  a  few  hints  we  have  at  present  no  clue  to 
its  real  physiological  value. 


CHAPTER  XIII. 


FOODS  AND  THEIR  PHYSIOLOGIC AL  VALUE. 

Having  thus  described  the  structure  of  the  organs  con- 
cerned in  digestion,  the  next  question  naturally  arising  is 
the  necessity  for  such  a  system.  The  body  is  a  machine, 
and  apart  from  the  mysterious  property  which  it  possesses, 
which  we  call  l'life,"  it  is  subject  to  all  the  physical  laws 
which  govern  other  machines.  We  may  even  go  further, 
and  say  that  although  we  do  not  understand  what  consti- 
tutes life,  all  experiments  force  us  to  the  belief  that  this  prop- 
erty itself  is  never  in  violation  of  physical  and  chemical 
laws.  Machines  must  be  supplied  with  energy  to  enable 
them  to  do  their  work.  There  must  be  the  pressure  of 
steam,  the  electro-motive  force  of  a  dynamo,  the  momentum 
of  running  water,  or  what  not,  to  set  things  in  motion.  As 
soon  as  the  source  of  energy  is  cut  off  the  machine  stops. 
The  idea  of  creating  a  perpetual-motion  machine,  one  which 
when  set  going  will  create  the  force  with  which  to  run,  is  a 
scientific  absurdity.  Not  only  have  thousands  of  failures  to 
construct  one  proved  that,  but  one  of  the  most  firmly  estab- 
lished laws  of  science,  possibly  one  of  the  most  fundamental 
discoveries  of  this  century,  has  been  the  law  that  energy 
can  neither  be  created  nor  destroyed.  This  law  is  called 
the  "  law  of  the  conservation  of  energy."  A  great  advance 
was  made  when  it  was  proved  that  the  energy  of  the  living 
body  is  subject  to  this  same  law.  Formerly  it  was  believed 
that  the  working  energy  of  the  body  was  a  mysterious  kind 
of  vital  force  which  seemed  to  be  in  continued  spontaneous 
creation  in  the  body.  It  may  be  said  that  the  real  science 
of  physiology  was  born  when  this  notion  was  abandoned. 

While,   however,   energy  is  indestructible  it  may  easily 
be  changed  from  one  form  to  another.    Steam  pressure  may 
(308) 


FOODS    AND    THEIR    PHYSIOLOGIC AL   VALUE.  309 

be  changed  to  motion,  this  in  a  motor  to  electricity,  the 
electricity  in  a  lamp  to  light,  in  a  coil  of  wire  to  magnetism, 
and  in  the  motor  of  the  street-car  back  again  to  motion. 
While  such  a  change  from  one  form  to  another  is  possible 
and  readily  accomplished,  the  change  so  made  is  always  in 
definite  and  fixed  proportions.  An  always  invariable  and 
fixed  amount  of  heat  is  changed  into  a  corresponding  cer- 
tain amount  of  motion,  or  vice  versa.  If  in  an  engine  run- 
ning a  factory,  lighting  and  heating  it  as  well,  every  bit  of 
energy  could  finally  again  be  collected  it  would  be  found  to 
be  identical  in  amount  with  the  original  energy  producing 
all,  even  though  in  the  meantime  it  might  have  passed 
through  a  half  dozen  other  forms.  The  forms  of  energy 
just  mentioned  have  been  forms  which  might  be  readily  rec- 
ognized "as  energy.  There  is  something  moving  or  dyna- 
mic about  the  current  of  electricity,  about  the  light  of  the 
lamp,  or  the  heat  in  the  furnace.  Such  evident  energies 
are  spoken  of  as  dynamic  or  kinetic  energies.  But  energy 
may  appear  in  a  latent  form.  A  barrel  of  gunpowder  or  a 
cartridge  of  dynamite,  although  neither  electrified,  nor 
heated  nor  in  motion,  possesses  a  large  amount  of  inherent 
energy.  But  a  small  spark  is  necessary  to  transform  what 
is  latent  into  energy  of  the  most  dynamic  kind.  Such  latent 
or  resting  energy  is  spoken  of  as  potential  energy.  The 
energy  which  comes  from  the  burning  of  wood  or  coal  is  of 
this  potential  kind. 

The  form  of  energy  most  suited  to  the  body  is  this  kind 
of  latent  energy.  It  can  be  easily  demonstrated  that  the 
food  constituting  an  ordinary  meal,  if  dried,  can  easily  be 
made  to  burn  and  yield  considerable  quantities  of  dynamic 
energy.  Sugar,  fats,  meats,  breads,  all  these  may  be  made 
to  burn  and  give  up  the  latent  energy  stored  in  them.  It  is 
this  energy  which  is  the  source  of  supply  to  the  body.  As 
far  as  our  knowledge  goes  now  it  has  been  impossible  to  get 
energy  apart  from  matter.  In  fact,  it  is  impossible  to  think 
of  energy  except  in  terms  of  matter,  and  energy  has  some- 
times been  defined  as  matter  in  motion,  in  which  the  motion 


310  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

may  be  either  a  motion  of  the  whole  mass,  a  molecular 
motion,  or  even  an  atomic  one.  For  this  reason  the  body 
which  desires  primarily  the  energy  to  make  possible  its 
activity,  must  take  into  itself  large  quantities  of  material  in 
which  the  energy  is  bound. 

So  far  we  have  considered  the  human  body  as  a  machine 
completely  constructed  and  needing  no  repair,  needing  only 
energy  to  run  it.  But  it  is  evident  that  there  are  other  ne- 
cessities for  introducing  outside  material  into  it.  For  many 
years  of  its  life  it  must  increase  in  size,  and  this  it  can  do  only 
by  appropriating  from  the  food  those  substances  which  it  can 
build  into  its  own  tissues.  Even  when  fully  matured  there 
is  a  continued  waste  which  needs  new  material  to  replace 
it.  The  necessity  for  foods,  therefore,  is  two-fold:  First, 
to  furnish  the  material  out  of  which  the  tissues  of  the  body 
may  be  constructed;  and,  secondly,  to  furnish  material  out 
of  which  the  body  may  derive  the  energy  required  for  its 
activity.  In  order  to  understand  how  much  this  shall  be, 
it  is  desirable  to  examine  what  the  losses  of  the  body  are 
under  normal  conditions. 

THE  LOSSES  OF  THE  BODY. 

1. — In  Matter.  Careful  investigations  upon  persons  of 
average  size  and  conditions  show  that  in  the  course  of  a  day 
there  is  lost  from  the  body  in  the  form  of  matter  about  nine 
pounds.  In  this  is  not  included  that  undigested  portion  of 
the  food  which  never  really  becomes  part  of  the  body. 
About  five  pounds  of  this  loss  is  through  the  lungs.  It 
seems  at  first  surprising  to  think  that  even  in  so  short  a 
time  as  one  day  there  should  have  been  breathed  out  of  the 
lungs  a  quantity  of  gas  reaching  the  amount  of  about  five 
pounds.  It  seems  not  quite  so  surprising  that  about  three 
pounds  or  more  of  this  is  eliminated  from  the  kidneys. 
The  remainder  is  thrown  off  from  the  skin  or  poured  as  ex- 
cretions into  the  alimentary  canal.  Evidently,  therefore, 
from  the  mere  standpoint  of  matter  it  is  necessary  to  put 
into  the  body  each  day  nine  pounds  of  suitable  substances 


FOODS    AND    THEIR   PHYSIOLOGIC AI,   VALUE.  311 

capable  of  replacing  these  nine  pounds  of  loss.  The  sub- 
stances lost  from  the  body  are,  in  the  lungs,  carbon  dioxide 
and  watery  vapors;  in  the  kidneys,  water  and  a  number  of 
nitrogenous  substances  and  salts;  and  from  the  skin,  water 
and  salts  mainly.  The  losses  of  the  body  in  excretions  poured 
into  the  intestinal  canal  are  certain  ingredients  of  the  bile, 
to  be  discussed  later.  Possiby  one  ought  to  add  in  this  con- 
nection occasional  losses  of  the  cuticle  of  the  skin  or  epi- 
thelium cells  from  the  mouth,  which,  however,  do  not 
figure  in  a  material  sense  in  this  calculation. 

2. — In  Energy.  In  energy  the  losses  of  the  body  are 
mainly  of  two  kinds.  By  far  the  greater  part  of  the  energy 
is  expended  in  the  form  of  heat.  A  relatively  small  pro- 
portion of  it  gives  rise  to  muscular  motion.  It  is  a  matter 
of  interest  that  in  our  bodies  about  one-fifth  only  of  all  the 
energy  is  utilized  in  muscular  activity ;  but  four-fifths  in  the 
maintenance  of  the  bodily  temperature.  While  this  seems 
but  a  small  per  cent.,  it  is  much  greater  than  in  even  the 
best  of  engines,  the  amount  of  energy  in  these  to  be  util- 
ized in  actual  motion  being  from  one-eighth  to  one-tenth, 
while  in  the  ordinary  engines  possibly  not  more  than  one- 
fifteenth  or  one-twentieth  is  utilized.  When  one  remembers 
that  in  a  locomotive  only  one  bushel  of  coal  out  of  ten  is 
really  expended  in  pulling  the  train,  and  the  other  nine  lost 
in  heating  the  engine  and  in  friction,  one  is  tempted  to 
believe  that  the  most  helpful  discoveries  of  the  future  may 
be  in  enabling  us  to  realize  a  greater  per  cent,  of  the  energy 
in  active  work. 

The  amount  of  heat  lost  by  an  average  person  in  one 
day  is  tolerably  difficult  to  determine.  Experiments  have, 
however,  been  made,  the  result  of  which  show  that  if  all  the 
heat  radiated  from  a  working  body  in  one  day  were  collected 
it  would  be  sufficient  to  raise  the  temperature  of  about  100 
pounds  of  water  from  zero  to  the  boiling  point.  This,  too, 
seems  at  first  too  much  when  we  remember  that  the  tem- 
perature of  the  body  remains  fairly  constant,  rarely  exceed- 
ing that  of  98  degrees  Fahrenheit.  It  must,  however,  be  borne 


312  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

in  mind  that  this  temperature  is  maintained  by  a  continued 
radiation  of  heat  from  the  body,  or  by  a  loss  of  heat  in  the 
evaporation  of  the  sweat  of  the  skin.  Such  a  continued 
loss  during  twenty-four  hours  would  not  be  inconsiderable. 
Evidently,  therefore,  to  replace  this  loss  of  energy  there 
must  be  introduced  into  the  body  as  food,  substances  which 
when  they  are  burned  will  give  the  amount  of  heat  required, 
and  of  course  in  addition,  the  energy  required  for  the  move- 
ment of  the  muscles,  which,  as  stated,  is  about  one-fifth 
more  in  amount. 

In  giving  as  the  losses  in  energy  muscular  activity  and 
heat,  no  attention  is  paid  to  other  possible  forms  of  energy 
in  connection  with  secretion,  or  with  the  nervous  system. 
In  the  former  there  are  probably  no  other  forms  of  energy 
concerned,  while  what  the  nature  of  the  energy  is  in  nerves 
and  psychic  states  we  are  at  present  perfectly  unable  to 
state.  That  such  states  are  accompanied  by  the  production 
of  heat  is  a  known  fact,  but  that  all  the  energy  is  trans- 
formed into  heat  is  another  question. 

The  exact  manner,  now,  in  which  the  body  is  able  to 
appropriate  these  foods  and  build  them  up  into  its  own  tis- 
sues, or  the  manner  in  which  it  derives  from  these  foods 
the  energies  it  expends,  will  be  more  fully  discussed  in  the 
chapter  on  nutrition. 

THE  CLASSES  OF  FOODS. 

It  would  be  entirely  out  of  place  here  to  enumerate  the 
large  list  of  substances  which  figure  as  foods.  These  are 
sufficiently  familiar.  A  study  of  the  varied  menu  of  our 
tables  shows  that  all  foods  may  be  divided  into  a  few 
typical  classes  in  which  the  foods  of  a  class  not  only  close- 
ly resemble  each  other,  but  in  which  those  of  one  class 
are  clearly  distinguishable  from  those  of  any  other.  These 
classes  are,  first,  albumens,  or  proteids;  second,  albumin- 
oids; third,  carbohydrates;  fourth,  hydrocarbons;  fifth,  in- 
organic salts;  sixth,  zvater. 


FOODS   AND   THEIR   PHYSIOLOGICAL,  VALUE.  313 

1. — The  Proteids.  The  proteids,  or  albumens,  are  foods 
characterized  by  containing  nitrogen  in  composition.  For 
this  reason  they  are  frequently  spoken  of  as  the  nitrogenous 
foods.  In  addition  to  the  nitrogen  they  contain  carbon, 
oxygen,  hydrogen,  and  traces  of  other  elements.  The  pro- 
teids are  familiar  in  the  form  of  egg  albumen,  myosin  or 
the  lean  of  meat,  casein,  the  substance  of  cheese,  gluten, 
the  main  ingredient  of  the  grains  or  cereals,  and  legumen,  a 
vegetable  albumen  found  in  relatively  great  proportion  in 
peas  and  beans.  All  the  albumens  of  our  diet  probably  fall 
into  one  or  the  other  of  these  classes.  Meats  of  different 
sources  are  physiologically  alike  and  differ  only  in  the  mat- 
ter of  flavor  and  digestibility ;  hence  all  forms  of  meat  would 
be  included  under  the  term  "myosin." 

These  foods  are  the  main  and  substantial  foods,  and 
have  always  been  recognized  as  the  essential  foods,  with- 
out one  or  more  of  which  it  would  be  impossible  to  live. 
Evidently  one  purpose  of  foods  is  to  make  new  tissues;  but 
the  tissues,  in  fact  protoplasm  wherever  found,  contains 
nitrogenous  substances  closely  allied  to  proteids  and  albu- 
mens, and  so  it  is  absolutely  necessary  that  to  produce 
these  in  the  body,  nitrogenous  foods  must  be  taken.  In 
the  carbohydrates  and  hydrocarbons  there  is  no  nitrogen, 
and  consequently  if  our  diet  should  consist  wholly  of  these 
the  tissues  of  the  body  would  gradually  waste  away  and  a 
death  by  starvation  would  ensue.  But  these  proteids  or  al- 
bumens do  not  figure  as  tissue  builders  only  in  the  body. 
They  are  an  integral  source  of  energy.  Without  trying  to 
press  an  analogy,  it  may  be  helpful  to  recall  that  many  sub- 
stances having  nitrogen  in  combination  are  peculiarly  well 
fitted  as  sources  of  energy.  One  needs  only  to  think  of 
gun-powder  with  its  contained  nitre,  or  of  nitro-glycerine 
with  its  contained  nitrogen,  or  of  a  number  of  other  energy- 
yielding  substances  which  depend  for  this  property  largely 
upon  the  fact  that  they  have  in  their  composition  nitrogen. 
Disregarding  here  numerous  objections  which  the  chem- 
ist might  urge,  it  may  be  said  that  like  these  formidable 


314  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

explosives  the  nitrogenous  proteids  of  the  body  are  a  mild 
form  of  explosive  out  of  which,  under  proper  circumstances, 
large  amounts  of  energy  may  be  utilized.  The  discussion 
of  the  manner,  however,  in  which  it  is  believed  to  be  done 
is  postponed  to  the  chapter  on  nutrition. 

2. — The  Albuminoids.  The  albuminoids  resemble  the 
albumens  or  proteids  in  containing  nitrogen.  The  nitrogen, 
however,  seems  in  such  a  combination  as  not  to  be  avail- 
able to  the  body  as  food,  as  it  is  in  the  case  of  the  proteids. 
For  this  reason  the  albuminoids  are  not  able  to  replace  the 
proteids.  The  most  familiar  example  of  the  albuminoids  is 
gelatine  found  in  soups  or  used  in  numerous  desserts.  This 
gelatine  is  derived  from  the  connective  tissues..  It  contains 
carbon,  oxygen,  hydrogen,  nitrogen,  and  traces  of  other 
substances,  resembling,  therefore,  as  just  stated,  the  pro- 
teids ;  but  the  contained  nitrogen  seems  not  to  be  assimila- 
ble by  the  tissues,  and  so  this  food  must  figure  in  the 
body  rather  like  a  non-nitrogenous  than  a  nitrogenous  food. 
Regularly,  however,  the  amount  of  albuminoids  taken  as 
food  is  so  small  that  it  does  not  figure  materially  in  the 
economy  of  the  body  at  all. 

3. — Carbohydrates.  In  the  carbohydrates  are  included 
the  starches  and  sugars.  The  name  "carbohydrates" 
naturally  suggests  carbon  and  water  as  entering  into  their 
composition,  and  such  is,  in  a  certain  sense,  true.  All 
carbohydrates  are  composed  of  carbon,  hydrogen  and  oxy- 
gen, but  the  hydrogen  and  oxygen  are  present  in  the  pro- 
portion of  water;  that  is,  two  atoms  of  hydrogen  to  every 
one  atom  of  oxygen.  An  important  point  is  that  they  con- 
tain no  nitrogen.  The  composition  of  the  commoner  car- 
bohydrates will  easily  explain  this.  Thus  the  composition 
of  cane  sugar  is,  Ci2  H22  On;  of  glucose,  Cc  Hi2  OG ; 
of  starch,  C6  H10  O3. 

The  physiological  value  of  these  foods  lies  in  the  fact 
that  they  figure  as  sources  of  energy.  It  will  be  pointed 
out  in  the  following  chapter  that  probably  the  main  source 


FOODS    AND    THEIR    PHYSIOLOGICAL   VALUE.  315 

of  muscular  and  heat  energy  is  derived  from  the  carbohy- 
drates. They,  too,  form  the  bulk  of  our  foods,  there  being 
few  dishes  indeed  of  which  either  the  starches  or  the  sugars 
do  not  form  an  integral  part.  In  addition  they  are  perhaps 
the  most  digestible  of  all  foods,  and  finally  a  reason  not  to 
be  neglected,  they  are  possibly  the  cheapest  of  foods.  It 
seems  a  rather  queer  coincidence  that  the  carbohydrates  are 
the  foods  best  suited  to  the  process  of  digestion,  best  suited 
as  sources  of  energy,  best  suited  to  the  palate,  and  finally, 
best  suited  to  our  expenses.  These  coincidences  are,  no 
doubt,  the  result  of  dietary  evolution.  The  close  relation- 
ship of  the  starches  and  sugars  is  evident  from  the  ease  with 
which  the  starches  are  changed  into  sugars  or  sugars  into 
starches. 

4. — Hydrocarbons.  In  the  hydrocarbons  are  included 
the  fats  and  oils.  As  indicated  by  their  name  they  contain 
mainly  hydrogen  and  carbon.  A  little  oxygen  is  also  in 
combination,  but  the  hydrocarbons  differ  essentially  from 
the  carbohydrates  in  the  fact  that  the  hydrogen  and  the 
oxygen  are  not  present  in  the  proportion  of  water.  Com- 
pared with  the  carbohydrates  the  hydrocarbons  contain  rela- 
tively more  carbon  and  hydrogen  and  less  oxygen.  For  this 
reason  when  they  are  burned  they  give  rise  to  much  more 
energy.  There  would  be  quite  a  material  difference  in  the 
amount  of  heat  liberated  between  the  combustion  of  a  bar- 
rel of  sugar  and  a  barrel  of  oil.  It  is  for  such  reasons  that 
the  fats  are  peculiarly  well  suited  as  a  diet  in  winter  or  in 
colder  climates,  and  the  Esquimau  who  drinks  his  blubber 
supplies  himself  with  one  of  the  best  foods  for  the  liberation 
of  heat.  The  distinction  between  fats  and  oils  is  a  rather 
arbitrary  one.  Hydrocarbons  which  at  ordinary  tempera- 
tures are  more  or  less  solid,  are  spoken  of  as  fats,  those  which 
at  these  temperatures  are  in  a  liquid  condition  are  called  oils. 

It  is  well  to  bear  in  mind  that  fats  contain  no  nitrogen, 
and  that  therefore  their  physiological  value  in  the  body  is 
similar  to  that  of  the  starches  and  sugars.  It  would  be  im- 
possible for  an  animal  to  live  long  if  its  diet  were  limited 


316  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

entirely  to  fats,  or  even  to  fats,  starches  and  sugars.  While 
the  fats  are  sources  of  greater  energy  than  the  carbohy- 
drates, and  so  better  suited  for  colder  climates,  they  seem 
not  so  well  suited  for  temperate  climates,  and  not  at  all  for 
tropical  regions.  Even  in  the  latitude  of  Indiana,  the  fats 
and  oils  have  not  nearly  the  general  food  value  of  the  car- 
bohydrates. Used  to  supplement  the  proteids,  starches  and 
sugars,  they  are  of  course  very  desirable.  The  commoner 
examples  of  the  hydrocarbons  are  butter,  lard,  tallow,  and 
the  vegetable  oils. 

5. — The  Inorganic  Salts.  In  the  common  use  of  the 
term  "  food,"  such  articles  as  common  and  other  inorganic 
salts  are  not  included,  but  there  is  as  much  of  a  necessity 
for  the  presence  of  some  of  these  salts  to  make  possible  the 
normal  functions  of  the  body  as  there  is  that  proteids,  sugars 
and  fats  shall  replace  the  waste.  With  the  exception  of 
common  salt,  which  is  added  as  a  special  ingredient,  usu- 
ally however  more  for  the  palate  than  for  its  physiological 
value,  the  other  inorganic  salts  reach  us  as  regular  ingredi- 
ents of  the  foods.  In  nearly  all  of  our  solid  foods  there  is 
a  small  proportion  of  mineral  matter.  This  may  easily  be 
demonstrated  by  burning  bits  of  these  foods.  There  are 
practically  no  foods  which  do  not  leave,  when  burned,  bits 
of  ash.  This  ash  of  course  constitutes  the  mineral  salts 
contained  in  the  original  substance.  While  all  of  these  salts 
do  not  find  their  way  into  the  body,  the  body  is  able  to  dis- 
solve and  assimilate  such  of  them  as  are  especially  needed 
in  the  work  of  the  tissues  for  the  building  up  of  mineral 
constituents  of  such  tissues  as  bone  or  enamel.  A  few  of 
the  commoner  mineral  salts  which  are  required  in  the  body 
are  here  given. 

For  the  growth  of  bone  there  are  required  salts  of  mag- 
nesium and  calcium  (lime) ;  for  the  haemoglobin  of  the 
blood,  traces  of  iron ;  for  the  blood  and  lymph  of  the  body, 
considerable  quantities  of  common  salt\  as  an  integral  por- 
tion of  the  red  corpuscles  and  other  tissues,  potash  salts. 


1-OODS    AND    THEIR    PHYSIOLOGICAL   VALUE.  317 

While  these  are  the  main  mineral  ingredients  a  chemical 
examination  of  the  body  would  reveal  small  traces  of  quite 
a  number  of  additional  inorganic  salts,  which  may  be  omit- 
ted here.  Not  only  are  these  salts  needed  to  build  up  the 
mineral  constituents  of  tissues,  such  as  bone  or  enamel,  but 
they  are  also  needed  to  make  possible  the  proper  working 
of  the  tissues.  Thus  it  is  known  that  animals  from  which 
common  salt  ha^s  been  kept  will  become  materially  deranged, 
suffering  what  is  called  a  "  salt  craze,"  and  the  continued 
withholding  of  the  salt  may  finally  induce  fatal  results.  The 
exact  manner  in  which  this  salt  figures  will  be  treated  fur- 
ther on. 

6. — Water.  On  account  of  its  abundance  and  free  access 
everywhere,  water  is  not  classed  as  a  food,  but  is  such  in 
an  essential  way,  although  of  course  no  energy  can  be  di- 
rectly derived  from  the  same  ;  but  as  an  agent  for  dissolving 
other  foods,  as  an  ingredient  forming  by  far  the  largest 
amount  of  all  the  tissues,  it  plays  a  first  role  in  digestion 
and  nutrition. 

A  MIXED  DIET. 

Very  few  of  the  foods  as  they  are  served  to  us  on  the 
dinner  table  belong  wholly  to  one  or  another  of  these 
classes.  In  nearly  every  case  they  are  mixtures  of  some  or 
all  of  them,  and  their  dietetic  value  will  depend  upon  the 
relative  proportions  in  which  they  contain  these  classes  as 
ingredients.  The  multitude  of  dishes  ranging  from  the 
highly  flavored  and  seasoned  ones  of  tables  of  plenty,  down 
to  the  simpler  foods  of  the  peasant's  meal,  are  but  mixtures 
in  varying  proportions.  The  different  character  which  the 
varying  dishes  possess  is  usually  much  more  a  matter  of 
flavor  or  condiment  than  it  is  a  matter  of  nutritive  value. 

In  order  to  fully  understand  the  nutritive  value  of  the 
food  then,  and  leaving  out  entirely  the  matter  of  flavor,  the 
influence  of  which  ceases  with  the  palate,  it  is  necessary  to 


318  STUDIKS    IN    ADVANCED    PHYSIOLOGY. 

make  an  analysis  of  these  mixtures  and  to  determine  the 
amounts  of  each  one  of  the  classes  just  mentioned.  The 
accompanying  table,  modified  slightly  from  Herman,  shows 
in  a  very  striking  way  the  composition  of  most  of  the  com- 
moner articles  of  food.  By  reference  to  it  it  will  be  seen 
that  the  animal  foods,  such  as  the  meats,  contain  very  little 
of  carbohydrates,  but  relatively  much  of  proteids  and  fat. 
Of  course  the  percentage  of  fat  will  vary  within  wide  lim- 
its, and  will  depend  largely  upon  the  condition  of  the  ani- 
mal examined.  The  leaner  the  animal,  evidently  the  less 
proportion  of  fat  and  the  relatively  larger  proportion  of  pro- 
teid.  On  the  other  hand,  meat  in  which  there  is  a  good 
deal  of  fat  might  finally  have  the  fat  in  excess  of  the  pro- 
teid,  a  condition  for  instance  found  in  ordinary  breakfast 
bacon.  For  this  reason  the  animal  foods,  that  is  the  meats, 
have  always  been  looked  i:pon  as  the  chief  sources  of  the 
nitrogenous  foods,  and  as  nitrogenous  foods  can  not  be  dis- 
pensed with  in  the  diet,  these  foods  have  become  popularly 
viewed  as  almost  if  not  wholly  indispensable. 

On  the  other  hand,  the  vegetable  foods  are  quite  sharply 
distinguished  by  their  relatively  large  amount  of  carbohy- 
drates and  rather  small  amounts  of  proteids  and  fats.  Thus 
the  food  value  of  the  potato  consists  almost  wholly  of  the 
starch  which  it  contains.  Rice  is  nearly  all  starch.  Even 
in  corn  the  starch  is  the  largest  ingredient,  although  in  it 
there  are  not  inconsiderable  quantities  of  proteid.  In 
wheat,  in  which  the  proteid  gluten  forms  quite  an  integral 
part  of  its  composition,  the  carbohydrates  occur  in  large 
proportion.  A  rather  remarkable  exception  of  what  has  just 
been  stated  occurs  in  the  composition  of  peas,  beans,  and 
other  leguminous  foods.  In  these  the  percentage  of  proteid 
actually  exceeds  that  found  in  meats.  This  explains  why 
these  vegetables  have  commonly  accredited  to  them  such  a 
high  nutritive  value,  and  why  sometimes  in  cases  of  mili- 
tary operations  when  it  is  difficult  to  transport  meats,  beans 
have  been  found  a  satisfactory  substitute. 


FOODS   AND    THEIR    PHYSIOLOGICAL   VALUE. 


319 


By  reference  to  the  table,  an  interesting  comparison 
may  be  made  between  the  composition  of  cow's  milk  and 
human  milk.  It  will  be  seen  that  cow's  milk  contains  rela- 
tively more  proteid,  but  on  the  other  hand,  less  sugar  and 
less  fat.  For  this  reason,  when  cow's  milk  is  to  be  rend- 


Beef  

T           i  I  i            1  I  I  !  I 

Mutton  
Pork  
Chicken  
Game  
Fish  

1  j  (  .         ( 

I                                                i||         ..|  1 

-_           g                    1  1  1  1  , 

—  i  —  :  —  r  1  1  1  1  1  1  
-  —  :  —  —  n  1  i  1  i  1  1  

Eggs  
Human  Milk  
Cow's  Milk  
Butter  
Cheese  

Beans  

"..           ...  ,!                      1                                                                                                                                                  1 

I  1  1  1  !  !  

-^^  ,  ,  ,  1  1  •  1  
'  i  1  i  i  i  i  i  ' 

9          10         2\0        30         l|0         5J0        60         ?|0         8\0        S\0        /6 

i                                       i                          i                          i         _ 

Peas  
Rice  

Wheat  Flour  

ii                                       ill       1  

f—  1                                                                            •                •     ••-"•  '.-     •.     '                        1 

Maccaroni  

-—  -J  '  !  '       •      .         .    -,      '  1 

Rye  Bread  

;     *        ...     '                '  ^—  ^T-  '  '  '  i 

Potatoes  

•i       •      •        E!                                                 ,-  ,  1 

Turnips  
Spinach  

i        ;ii                                                          ,.    .  1 
1             1             !             1             1             I         ...         —  1  u 

Fruit,  fresh  
Fruit,  dried  

] 

<fU                                                              -    •  '  .      •    1    L-L^          1  !  1 
M         20         30          ?0          SO         60         70          SO          30         JO 

txv^.?]         i..'..w.  i         i          i        SSUBR 
'roteids.           Fats.           Carbo-          Woody            Water            Ash. 
hydrates.        tissue. 

Fig.  125. — TABLE  GIVING  RELATIVE  COMPOSITION  OF  THE  COMMONER  FOODS. 

ered  as  nearly  of  the  composition  of  human  milk  as  possi- 
ble, it  is  diluted  with  water  in  order  to  dilute  the  extra 
amount  of  proteids  in  the  cow's  milk,  and  then  there  is  ad- 
ded cream  and  sugar  to  bring  these  up  to  the  increased  per- 
centage in  the  human  milk.  The  interested  reader  will  be 
able  to  answer  so  many  questions  bearing  directly  on  these 
points  here  under  consideration  by  referring  directly  to  the 
table  given,  that  an  extended  comment  on  the  composition 
of  the  commoner  foods  is  deemed  unnecessary. 


320  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

THE    EELATIVE    AMOUNTS    OF    THESE    CLASSES    OF   FOODS  RE- 
QUIRED BY  AN  AVERAGE  INDIVIDUAL  AND  THE 
VALUE  OF  A  MIXED  DIET. 

The  experience  of  every  one  has  shown  that  it  is  not 
desirable  to  limit  one's  diet  exclusively  to  one  kind  of  food. 
If  one  had  nothing  but  meat  he  would  get  much  more  nitro- 
gen than  would  be  necessary  in  trying  to  get  the  amount  of 
carbon  which  the  body  requires,  the  relative  amount  of  car- 
bon being  so  small  in  the  proteids.  If  one  limited  his  diet 
to  a  substance  which  was  rich  in  fats  and  sugars,  but  con- 
tained only  traces  of  nitrogen,  he  would  have  to  eat  un- 
necessarily large  quantities  of  fats  and  sugars  to  get  the 
proteid  necessary  for  his  body.  The  most  sensible  way, 
therefore,  of  determining  the  composition  of  one's  diet  is  to 
take  enough  proteid  food  to  give  to  the  body  all  the  nitro- 
genous food  it  needs,  and  then  to  supply  it  further  with  the 
necessary  amounts  of  carbon  and  hydrogen,  to  take  foods 
especially  rich  in  these,  such  as  fats  and  sugars. 

A  very  natural  question  is:  What  are  the  relative 
amounts  of  these  classes  of  foods  which  an  average  working 
body  needs,  say  in  a  day?  A  great  many  and  careful  ex- 
periments have  been  made  and  the  results  of  these  do  not 
vary  materially.  We  may,  therefore,  give  the  average  fig- 
ures with  much  probability  that  they  state  the  correct  con- 
dition of  things.  In  an  experiment  by  Pettenkofer  and  Voit 
on  a  workingman  twenty-eight  years  old,  weighing  about 
150  pounds,  it  was  found  that  when  not  at  work  he  needed 

137  grams  of  proteid. 
72  grams  of  fat. 
352  grams  of  carbohydrates. 

On  a  day  when  this  same  workman  was  at  regular  work  he 

consumed 

137  grams  of  proteid  (same  as  when  at  rest). 

173  grams  of  fat. 

352  grams  of  carbohydrates. 

It  will  be  noticed  that  the  extra  work  entailed  an  extra  con- 
sumption of  fat.  Other  observers  have  changed  this  experi- 
ment just  'a  little.  They,  too,  found  that  the  amount  of 


FOODS   AND   THEIR    PHYSIOLOGICAL   VALUE.  321 

proteids  needed  either  at  work  or  at  rest  was  about  the 
same.  They  did  not,  however,  increase  the  amount  of  fat 
given  when  working,  but  made  the  increase  in  the  carbo- 
hydrates, and  then  found  that  under  such  circumstances 
the  man  to  be  satisfied  consumed  much  larger  quantities  of 
these. 

Similar  experiments  were  tried  on  a  young  physician, 
whose  diet  in  one  day  consisted  of: 

127  grams  of  proteid. 
89  grams  of  fat. 
362  grams  of  carbohydrates. 

As  average  figures,  therefore,  the  following  little  table  may 

suffice : 

Water 3,000  grams. 

Proteids 131      " 

Fats 88 

Carbohydrates 400     " 

In  such  an  average  diet  there  are  20  grams  of  nitrogen  and 
312  grams  of  carbon.  This  proportion  is  about  the  propor- 
tion normally  desired  by  the  body.  These  20  grams  of  ni- 
trogen could  be  secured  from  the  following  amounts  of 

foods : 

Cheese- 272  grams. 

Peas 520     " 

Lean  meat 538 

Wheat  flour 800 

Eggs 900  (about  18  eggs.) 

Milk 3,000 

Potatoes 4,600 

Turnips ~ 8,700 

A  glance  at  the  figures  just  shown  will  give  at  once  the 
relative  nutritive  value  of  the  main  foods.  Cheese,  consist- 
ing almost  wholly  of  casein  and  being  in  tolerably  compact 
form,  is  probably  by  weight  the  most  nutritious.  Eggs,  on 
the  other  hand,  in  spite  of  our  notion  that  they  are  so  nu- 
tritious, would  not  yield  to  the  body  the  required  amount 
of  nitrogen  unless  the  diet  should  average  eighteen  or  more 
eggs  per  day.  In  order  to  get  sufficient  proteids  out  of  a 
diet  of  potatoes  it  would  require  the  consumption  of  a  per- 
fectly unwieldy  lot,  while  if  the  attempt  should  be  made  to 
21 


322  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

get  the  necessary  amount  of  proteids  from  turnips,  for  in- 
stance, an  amount  not  less  than  8,700  grams  would  have  to 
be  consumed  each  day.  Evidently,  therefore,  it  is  desira- 
ble that  the  body  should  derive  its  nitrogen  supply  from 
those  foods  which  appear  first  in  the  table  just  given. 

The  312  grams  of  carbon  which  on  an  average  the  body 
needs  per  day  might  be  derived  from  the  following  amounts 
of  foods: 

Fat  meat  450  grams. 

Corn  meal 800     " 

Wheaten  flour 824 

Rice 900 

Peas 1,000 

Cheese 1,200 

Eggs 2,200  (about  43  eggs.) 

Lean  meat 2,600 

Potatoes 3,100 

Milk 4>6oo 

Turnips 10,000 

These  figures  at  once  give  us  a  clue  as  to  the  most 
desirable  kind  of  a  diet.  It  will  evidently  consist  first,  of 
one  or  more  of  those  substances  which  are  very  rich  in  pro- 
teid,  such  as  cheese,  peas  or  beans,  meat,  cereal  flour  or 
eggs,  in  order  to  get  the  proper  nitrogen  supply,  and  then 
for  the  carbon  needed  to  turn  to  the  second  table  and  get 
either  the  fat  meats  which  are  especially  rich  in  carbon,  or 
else  some  of  the  more  starchy  foods  like  corn,  wheat,  rice 
or  potatoes. 

FLAVOES,   CONDIMENTS,  AND  STIMULANTS. 

In  describing  the  classes  of  foods  so  far,  it  has  been 
done  without  very  much  attention  to  the  distinctions  which 
the  palate  would  make.  In  the  actual  eating  of  foods  these 
secondary  flavors  and  condiments  not  infrequently  play 
a  very  determining  role.  However,  all  these  flavors,  no 
matter  how  pleasant  they  may  be  to  the  palate,  have  prac- 
tically no  digestive  value  at  all,  and  so  for  pure  physio- 
logical reasons  need  not  be  considered.  The  dainty  dis- 
tinctions of  taste  which  the  various  kinds  of  meats  afford 


FOODS   AND    THEIR    PHYSIOLOGICAL  VALUE.  323 

cease  as  soon  as  the  food  has  passed  the  tongue.  Even 
the  hundred  and  one  varieties  of  flavors  of  our  fruits,  and  the 
artificial  flavors  of  our  desserts  share  the  same  fate.  Salt, 
of  course,  which  is  sometimes  viewed  as  a  seasoning  sub- 
stance figures  as  a  food,  but  the  peppers,  or  spices,  and  the 
mustards  are  foods  in  no  sense.  We  derive  no  nourishment 
from  them,  and  they  serve  merely  to  give  gist  to  the  taste, 
and  sometimes  by  their  stimulating  action  to  arouse  the 
often  too  dormant  digestive  organs.  To  this  same  class 
belong  the  teas  and  coffees.  These  now  almost  universal 
drinks  owe  their  popularity  to  peculiar  organic  compounds 
called  theine  and  caffeine,  respectively,  which,  while  of  no 
nutritive  value,  have  a  slight  stimulating  effect.  In  addition 
to  this  a  cup  of  hot  tea  or  coffee  during  meal  time  is  fre- 
quently quite  potent  to  arouse  the  stomach  to  secretion,  a 
result  which  might,  however,  be  equally  well  brought  about 
by  drinking  a  glass  of  hot  water.  The  rather  baneful 
effects  which  follow  from  an  excessive  use  of  these  are  too 
well  known  to  need  mention  here. 

ALCOHOL. 

Almost  .as  far  back  as  history  carries  us,  man  has  more 
or  less  generally  added  alcohol  in  some  of  its  forms  to  the 
articles  of  his  daily  consumption,. and  even  at  this  present 
day  the  wines  and  beers  are  in  many  places  regular  dishes 
at  the  table,  and  the  question  naturally  arises,  what  the  nu- 
tritive value  of  this  substance  is.  Alcohol  is,  of  course, 
never  taken  in  its  pure  form,  but  in  varying  grades  of  dilu- 
tion as  given  in  the  table  below: 

Rums  and  whiskies  from  60  to  80  per  cent. 
Brandies  "     40  to  60       " 

Wines  ranging  from         40  down  to  5  per  cent. 
Beers        "  "  4        "       i 

Ordinary  commercial  alcohol  is  a  colorless  liquid  of  a 
peculiar  penetrating  odor  and  of  a  very  inflammable  nature. 
It  is  used  in  the  arts  very  extensively  as  a  solvent  for  in- 
iminerable  substances,  and  in  the  sciences  it  is  used  in 


324  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

large  quantities  as  a  preserving  fluid  for   anatomical    and 
zoological  specimens. 

It  is  produced  by  a  process  called  fermentation.  This  is 
a  process  brought  about  by  a  little  plant  called  the  "yeast 
plant,"  which  by  its  action  upon  sugar  converts  it  into 
alcohol  and  carbon-dioxide  gas  and  several  minor  products. 
In  the  distillery  or  the  brewery  this  process  of  fermenta- 
tion is  allowed  to  go  on  until  the  desired  per  cent,  of  alco- 
hol has  been  reached.  The  carbon  dioxide  gas  is  allowed 
to  escape,  and  gives  to  the  fermenting  vats  their  frothy  or 
"brewing"  appearance.  The  condition  of  things  in  the 
making  of  yeast  bread  is  the  same.  Here,  too,  some  yeast 
which  has  either  been  specially  put  in,  or  else  allowed  to 
fall  in  from  the  air,  acts  upon  some  of  the  sugar  in  the 
dough,  resulting  in  the  formation  of  alcohol  and  carbon 
dioxide  gas.  The  carbon  dioxide  gas  in  its  attempt  to 
escape  from  the  dough  forms  innumerable  little  bubbles 
throughout  it,  and  so  causes  the  bread  to  "rise"  or  become 
light.  The  alcohol,  of  course,  evaporates  in  the  process  of 
baking.  The  same  thing  is  again  illustrated  in  the  famil- 
iar canning  of  fruits.  Here  the  fruit  to  be  preserved  is 
boiled,  the  primary  intention  of  which  is  to  destroy  all 
germs  and  all  yeast  plants  in  it,  and  then  the  fruit  before 
it  has  a  chance  to  cool  is  put  into  jars  and  these  then  her- 
metically sealed.  If,  however,  the  sealing  is  defective  and 
air,  as  we  say,  gets  in,  fermentation  is  soon  set  up  and  the 
sugar  in  the  fruit  is  ushered  along  in  the  process  towards 
the  formation  of  alcohol  and  remoter  substances.  It  is  not, 
however,  the  air  which  sets  this  process  going.  It  is  the 
introduction  of  some  yeast  plants  along  with  the  air  which 
is  the  source  of  the  trouble. 

The  chemical  and  physical  properties  of  alcohol  in  its 
various  forms  need  not  be  dwelt  upon  here,  the  primary 
question  in  this  instance  being  its  physiological  effects. 
This,  in  a  general  way,  is  its  apparent  stimulating  power. 
Administered  to  animals  it  quickens,  for  a  while  at  least, 
the  general  tone  of  nearly  all  the  organs.  It  produces  a  tem- 


FOODS    AND    THEIR    PHYSIOLOGICAL   VALUE.  325 

porary  exhilaration  which  is  pleasant,  and  which  no  doubt 
explains  the  desire  which  has  so  generally  prompted  man- 
kind to  use  it.  There  are  so  many  good  books  now  avail- 
able giving  the  detailed  and  specific  action  of  this  substance 
on  the  various  organs,  and  on  the  body  in  general,  that  such 
a  detailed  account  is  deemed  unnecessary  here.  That  alco- 
hol taken  in  excess  produces  derangements  of  the  most 
serious  nature  in  almost  all  the  organs,  is  a  point  which  no 
man  can  doubt  who  has  seen  the  brutish  drunkard  lying  in 
the  gutter.  Whether  alcohol  in  moderate  quantities  is  a 
food  or  not,  whether  in  small  amounts  it  may  not  be  helpful, 
is  a  question  which  does  not  concern  us  here.  Suffice  it  to 
say  that  all  physiology  and  possibly  all  medicine  has  shown 
conclusively  that  there  is  absolutely  no  necessity  for  a  sound 
man  to  add  alcohol  in  any  of  its  forms  to  his  daily  diet.  The 
person  who  persists  in  doing  so  must  seek  his  reason  else- 
where, while  the  fact  that  in  innumerable  instances  it  has 
done  unspeakable  harm,  is  equally  well  established.  With- 
out denying  for  a  moment,  or  disregarding  the  effect  of 
alcoholic  excesses  upon  the  various  tissues  of  the  body,  the 
point  remains  that  the  truest  reason  against  the  use  of  this 
substance  is  a  moral  one.  The  fact  that  the  heart  of  the 
toper  is  unnaturally  stimulated  by  his  whiskey,  is  a  very 
insignificant  fact  compared  with  the  more  serious  one  that 
this  whiskey  in  its  effects  has  broken  possibly  a  wife's  and 
a  mother's  heart;  the  fact  that  the  drinking  of  alcohol 
lowers  the  temperature  of  the  body  of  the  toper  is  a  very 
trifling  fact  compared  with  the  more  awful  one  that  it  has 
given  babies  cold  feet  for  want  of  shoes,  and  wives  cold 
backs  for  want  of  warm  clothing;  that  it  has  made  homes 
cold,  and  has  reduced  the  warmth  of  a  thousand  friends. 
The  fact  that  it  may  curdle  the  liver  is  of  small  conse- 
quence when  compared  with  the  more  serious  fact  that  it 
too  frequently  curdles  the  sentiments,  the  hopes,  and  the 
aspirations.  That  alcoholic  excesses  may  produce  the  ugly 
ulcerations  of  the  drunkard's  stomach  is  possibly  not  so 


326  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

lamentable  as  the  many  blotches  on  virtue  which  it  has  pro- 
duced in  our  industrial  civilization.  A  certain  firm  on  one 
Saturday  evening  paid  out  to  its  workingmen  four  hundred 
marked  ten-dollar  bills.  The  following  Monday  one  hun- 
dred of  these  marked  ten-dollar  bills  were  deposited  in  the 
city  banks  by  different  saloon  keepers  of  the  place.  When 
one  remembers  how  many  shoes,  how  many  dresses,  how 
many  pieces  of  nutritious  meat,  how  many  little  toys  for 
playful  children,  how  much  happiness,  in  short,  for  innu- 
merable homes  might  have  been  purchased  with  these  one 
hundred  marked  ten-dollar  bills  which  found  their  way  into 
the  saloons,  one  need  not  be  told  further  about  the  lament- 
able physiological  and  moral  effects.  A  mighty  step  in  the 
right  direction  will  have  been  made  when  every  young  per- 
son fully  realizes  that  by  avoiding  the  demon  of  drink  the 
chances  are  greater  that  he  will  always  have  an  abundance 
of  good  friends,  that  he  will  be  able  to  enjoy  what  is  best 
in  life,  that  he  will  be  a  helpful  member  of  his  community 
and  that  he  will  always  have  a  dollar  in  his  pocket  with 
which  to  buy  bread  for  himself  and  his  own. 


CHAPTER  XIV. 


DIGESTION  AND  THE  DIGESTIVE  AGENTS. 

HISTORICAL. 

Our  knowledge  concerning  the  process  of  digestion  does 
not  reach  back  very  far.  The  notion  of  the  ancients  was 
very  primitive  indeed.  They  likened  the  digestion  in  the 
body  to  a  kind  of  cooking,  and  in  the  middle  ages  this 
notion  was  carried  so  far  that  they  actually  thought  one 
purpose  of  the  animal  heat  of  the  body,  especially  the 
warmth  of  the  internal  organs,  was  to  cook  the  foods.  It 
was  as  late  as  the  seventeenth  century  before  definite  notions 
of  digestive  ferments  in  the  stomach  arose ;  but  these  fer- 
ments were  looked  upon  as  causing  only  a  very  fine  me- 
chanical separation  of  the  food.  However,  Reaumur,  in 
1752  proved  that  the  agent  of  digestion  was  the  gastric 
juice,  and  that  this  digestion  could  be  accomplished  with- 
out any  mechanical  helps.  The  sour  re-action  which  Reau- 
mur had  noticed  was  established  by  Prout  in  1834,  to  be 
due  to  free  hydrochloric  acid.  Two  years  later,  in  1836, 
Schwann  discovered  the  pepsin.  In  1834  a  Canadian  by 
the  name  of  Beaumont  was  enabled  to  make  a  series  of  ob- 
servations on  a  man  whose  stomach  had  been  exposed  by  a 
wound,  and  upon  which  the  digestive  processes  could  be 
fairly  accurately  followed.  In  the  same  year  Eberle  suc- 
ceeded in  making  artificial  gastric  juice,  and  conducted 
experiments  in  digestion  with  the  same.  The  sugar-forming 
action  of  the  saliva  was  discovered  by  Leuchs  in  1831.  Our 
knowledge  of  the  digestive  processes  in  the  intestine  did 
not  begin  until  1848,  when  Claude  Bernard  established  the 
fact  that  pancreatic  juice  digested  fats.  Nine  years  later, 
in  1857,  Corvisart  discovered  that  pancreatic  juice  digested 

(327) 


328  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

proteids.  Although  first  discovered  by  Corvisart  the  pro- 
teid-digesting  nature  of  pancreatic  juice  was  finally  worked 
over  and  established  with  its  present  exactness  by  Ku'hne 
in  1867.  The  intestinal  juice  was  first  secured  in  a  pure 
form  by  Thiry  in  1865. 

THE  DIGESTIVE  AGENTS. 

We  have  now  to  consider  the  various  changes,  chemical 
and  physical,  by  means  of  which  the  solid  and  usually  in- 
soluble food  is  converted  into  a  liquid  form,  suitable  to  be 
absorbed  from  the  walls  of  stomach  and  intestine  and  passed 
into  the  blood.  The  process  of  digestion  begins,  of  course, 
in  the  mouth.  No  attention  is  here  paid  to  peculiar  changes 
helpful  in  the  process  of  digestion  which  have  been  brought 
about  by  the  cooking  or  baking  of  the  intended  food.  Thus 
it  is  a  familiar  fact  that  the  crust  of  bread  is  more  digest- 
ible than  the  inner  part,  the  process  of  baking  having 
changed  the  starch  in  question  into  a  form  which  is  more 
easily  soluble.  The  first  step  in  the  digestion,  as  far  as  the 
body  is  concerned,  is  that  of  mastication.  This  is  merely 
a  mechanical  process  by  means  of  which  the  food  is  broken 
up  and  so  enabled  to  be  swallowed.  During  the  process  of 
mastication,  however,  the  food  is  mixed  with  the  first  of 
the  digestive  fluids,  called  the  "saliva."  The  salivary 
ducts  of  the  parotid  and  submaxillary  glands  open  at  the 
base  of  the  molar  teeth  and  are  so  arranged  that  bits  of 
saliva  are  introduced  whenever  the  molars  are  inserted  into 
a  morsel  of  food.  In  addition  to  this,  of  course,  a  good 
deal  of  saliva  flows  into  the  front  part  of  the  mouth  from 
the  sublingual  gland,  and  is  there  more  or  less  thoroughly 
mixed  by  the  rotating  action  of  the  tongue. 

1. — Saliva  and  Salivary  Digestion.  Saliva  is  a  clear, 
transparent  liquid  when  filtered.  When  taken  from  the 
mouth  it  is  somewhat  cloudy,  owing  to  the  fact  that  it  has 
solid  substances  in  it:  bits  of  food  and  epithelial  cells  which 
have  been  detached  from  the  mucous  membrane  of  the 


DIGESTION    AND   THE    DIGESTIVE   AGENTS.  329 

mouth.  Very  frequently,  too,  \vhite  cells,  probably  identi- 
cal with  white  blood  corpuscles  are  present.  These  are 
corpuscles  which  have  probably  wandered  out  from  deeper 
tissues  along  with  the  secretion.  They  have  been  called 
salivary  corpuscles,  although  now  recognized  as  nothing 
more  than  escaped  leucocytes.  Saliva  is  a  little  heavier 
than  water  and  is  alkaline.  The  quantity  secreted  in  a  day 
is,  of  course,  subject  to  the  widest  variations,  varying  from 
200  to  2,000  grains.  Saliva  contains  the  following  constitu- 
ents in  1,000  parts: 

Water 994-2 

Mucin 2.2 

Ptyalin 1.3 

Inorganic  Salts 2.2 

The  inorganic  salts  are  largely  chloride  of  potassium  and 
sodium,  and  phosphates  of  calcium  and  magnesium.  These 
inorganic  salts  in  the  saliva  are  interesting  from  the  fact 
that  small  amounts  of  them  are  deposited  around  the  teeth 
and  give  rise  to  the  formation  of  tartar.  The  mucin  pres- 
ent in  the  saliva  is  ordinary  mucus  or  phlegm,  and  is  really 
an  addition  to  the  saliva  from  the  mucous  glands  in  the 
mouth.  This  mucus  has  no  distinct  value  further  than  that 
by  its  ropy  and  sticky  nature  it  serves  to  hold  bits  of  the 
food  together  and  so  makes  swallowing  easier.  Incidentally 
along  with  the  saliva  it  serves  to  keep  the  mouth  moist. 
The  main  and  distinct  constituent  of  saliva  is  the  ptyalin. 
This  belongs  to  the  class  of  substance  called  enzymes,  or 
ferments,  and  has  the  property  of  being  able  to  convert 
starch  into  sugar. 

THE  THEORY  OF  HYDROLYSIS. 

As  the  term  "enzyme"  or  ferment  occurs  repeatedly  in 
physiology  (the  pepsin  in  the  stomach,  the  trypsin  in  the 
pancreas,  and  others  being  ferments),  a  word  in  explana- 
tion of  these  substances  and  the  manner  in  which  they  are 
supposed  to  act  is  given. 

There  are  two  kinds  of  ferments;  one,  that  of  living  fer- 
ments, of  which  the  many  forms  of  bacteria  and  the  yeast 


330  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

plant  are  good  illustrations.  These  ferments  are  really  liv- 
ing beings  which  are  able  in  some  way  to  set  up  chemical 
processes  which  we  have  chosen  to  call  fermentation  pro- 
cesses. The  other  class  consists  of  unorganized,  dead  sub- 
stances. They  are  chemical  ferments.  To  this  second 
class  belong  almost  all  the  digestive  ferments  of  the  body. 
Ferments  have  the  power  of  breaking  up  certain  substances 
and  changing  them  into  new  compounds.  Thus  ptyalin, 
as  just  stated,  changes  starch  into  sugar.  It  is  probable 
that  these  ferments  produce  these  results  in  the  following 
way :  They  cause  the  substance  to  be  changed  to  take  up 
one  or  more  molecules  of  water,  and  then  split  this  combi- 
nation into  two  or  more  smaller  bodies.  This  action  is  well 
shown  in  the  change  which  takes  place  in  cane  sugar.  Not 
infrequently  cane  sugar  is  changed  into  two  sugars  called 
dextrose  and  levulose.  This  change  from  cane  sugar  to 
dextrose  and  levulose  is  represented  chemically  in  the  fol- 
lowing equation: 

Cin  H22  On+H2  0  =  C6  H12  06  +  C6  H12  O6 
Cane  Sugar  -f  Water  =  Dextrose  +  L,evulose. 

A  similar  change  occurs  in  the  mouth.  Under  the  in- 
fluence of  the  ptyalin  the  starch  is  made  to  combine  chem- 
ically with  more  water  and  the  resulting  molecule  is  then 
split  up,  sugar  being  the  result.  Ptyalin  is  present  in  many 
of  the  lower  animals,  especially  the  herbivorous  animals, 
but  seems  to  be  absent  in  the  carnivora.  It  was,  until 
recently,  believed  that  the  sugar  which  resulted  from 
the  action  of  the  ptyalin  on  starch  was  ordinary  grape 
sugar,  but  later  investigation  has  shown  that  this  is  in- 
correct, and  that  the  resulting  sugar  is  maltose,  a  sugar 
very  closely  related  chemically  to  ordinary  cane  sugar. 
However,  the  starch  is  not  at  once  changed  into  maltose,  but 
there  seems  to  be  between  the  beginning  starch  and  the 
final  maltose  a  number  of  intermediate  stages  with  which, 
however,  in  this  elementary  treatise  we  are  not  concerned. 

The  physiological  value  of  ptyalin  is  evident.  Starch  is 
insoluble,  and  could  not  pass  through  the  walls  of  the  ali- 


DIGESTION    AND    THE    DIGESTIVE    AGENTS.  331 

mentary  canal,  but  by  its  conversion  into  maltose  this  diffi- 
culty is  at  once  remedied,  maltose  being  quite  dialyzable. 
On  account  of  the  short  time  during  which  the  food  remains 
in  the  mouth  but  a  very  small  part  of  the  starch  is  con- 
verted into  maltose.  But  we  shall  see  in  the  discussion  of 
the  pancreas  that  this  process  is  again  picked  up  in  the  in- 
testine and  there  completed.  The  ptyalin  is  unable  to  act 
in  an  acid  medium,  and  so  as  soon  as  the  food  reaches  the 
stomach  its  digestive  action  ceases,  but  when  later  the  food 
is  passed  into  the  small  intestine  and  the  acid  of  the  stom- 
ach gives  way  to  the  alkalinity  of  the  intestine,  the  saliva 
renews  its  digestive  action,  so  that  possibly  the  greatest  ef- 
fect of  the  saliva  is  produced,  not  in  the  mouth,  but  in  the 
intestine.  The  digestive  action  of  the  ptyalin  may  be  easily 
demonstrated  by  taking  a  dish  of  boiled  starch  and  adding 
a  little  saliva  containing  ptyalin  to  it.  By  keeping  this  dish 
then  at  a  temperature  of  about  98°  Fahrenheit  the  starch  is 
rapidly  converted  into  sugar  and  may  be  detected  quite 
easily  by  the  taste  and  by  chemical  re-actions. 

2. — The  Stomach  and  Gastric  Digestion.  The  process 
of  digestion  in  the  stomach  is  almost  wholly  a  chemical  one 
and  is  only  incidentally  mechanical.  The  food  remains 
here  one  or  more  hours,  varying  with  its  digestibility,  dur- 
ing which  time  it  is  subjected  to  a  slight  churning  process. 
Slight  peristaltic  movements  creep  across  the  stomach,  the 
effect  of  which  is  to  more  or  less  mix  and  re-mix  the  gas- 
tric contents  and  so  materially  aid  the  juice  in  reaching  all 
the  particles  of  the  food.  The  stomach  owes  its  power  to 
digest  to  the  gastric  juice.  This  juice  is  by  no  means  a 
simple  substance,  but  is  a  mixture  of  several  things.  Its 
composition  is  in  1,000  parts  about  as  follows: 

993  parts  water. 

2  "     hydrochloric  acid. 

3  "      pepsin. 
2     "     salts. 

In  addition  to  these  substances,  which  can  be  more  or  less 
quantitatively  determined,  there  are  present  in  the  gastric 


332  STUDIES    IN    ADVANCED    PHYSIOLO'GY 

juice  several  other  substances  which  it  is  not  yet  possible  to 
secure  in  a  pure  form,  but  the  presence  of  which  can  be 
easily  demonstrated  by  the  actions  which  they  exert.  One 
of  these  is  the  ferment  called  "rennet,"  a  ferment  which 
coagulates  milk.  Traces  of  mucin  also  are  present. 

a. — Pepsin.  The  principal  ingredient  of  gastric  juice 
is  the  ferment  called  "pepsin."  This  is  an  organic  com- 
pound of  an  albuminous  nature,  possessing  almost  all  the 
characteristics  of  ordinary  peptones.  It  has  the  property 
of  digesting  albumens  and  albuminoids,  transforming  the 
albumens  into  soluble  peptones  and  the  albuminoids  into 
dialyzable  gelatin.  It  is  able  to  effect  these  changes,  how- 
ever, only  in  an  acid  solution,  which  explains  the  presence 
of  the  free  hydrochloric  acid  in  the  stomach.  In  fact,  it  is 
possible  that  the  pepsin  and  the  acid  may  in  conjunction, 
as  a  pepsin-acid,  effect  these  changes. 

The  change  from  the  non-dialyzable  and  sometimes  solid 
proteids  to  the  liquid  and  dialyzable  peptones  is,  however, 
not  a  direct  one.  As  in  the  case  of  the  conversion  of  sugar 
into  maltose  by  the  ptyalin  so  here  there  are  between  the 
beginning  proteids  and  the  final  peptones  a  number  of 
intermediate  stages  designated  as  acid  albumens  and  pro- 
teoses.  By  the  experiments  of  Kiihne  and  Chittenden  quite 
a  number  of  these  intermediate  products  have  been  deter- 
mined and  studied,  and  these  experimenters  have  worked 
out  a  table  showing  the  stages  through  which  the  proteids 
pass  toward  the  final  peptones.  However,  in  an  elementary 
text-book  these  changes  are  too  intricate  to  be  dwelt  upon, 
the  significant  fact  being  that  a  large  part  of  the  proteids 
of  the  stomach  are  converted  by  the  continued  action  of  the 
gastric  juice  into  peptones,  while  the  intermediate  stages 
and  any  proteids  not  affected  by  the  gastric  digestion  are 
passed  into  the  intestine  and  there  their  change  into  pep- 
tones is  completed  by  the  action  of  the  pancreatic  juice. 

.    It  must  not  be  understood   that  a  proteid  is   merely  a 
solid  albumen  and  a  peptone  a  liquid  albumen.     The  vital 


DIGESTION    AND    THE    DIGESTIVE    AGENTS.  333 

difference  between  a  proteid  and  a  peptone  is  in  the  power 
of  dialysis.  A  proteid  dialyzes  little  if  at  all,  while  a  pep- 
tone does  so  readily.  Egg  albumens  even  when  in  a  liquid 
form,  as  we  find  it  in  an  egg  which  has  been  subjected  to 
the  process  of  incubation  for  several  days,  is  by  no  means  a 
peptone.  In  spite  of  its  liquid  form  it  is  but  little  dia- 
lyzable,  and  if  taken  into  the  alimentary  canal  would  have 
to  be  transformed  into  dialyzable  peptones  in  no  less  a  way 
than  a  bit  of  solid  meat.  Peptones  further  possess  the 
property  of  not  being  coagulated  when  subjected  to  heat. 
This  is,  of  course,  also  true  of  certain  proteids;  as,  for  in- 
stance, the  proteid  in  milk  which  may  be  boiled  without 
coagulating  the  milk.  But  the  peptones,  in  addition  to  not 
being  coagulated  by  boiling,  are  not  precipitated  when 
treated  with  alkalies,  mineral  acids  or  various  salts.  In 
short,  a  peptone  is  an  albumen  in  such  a  liquid  form  that  it 
is  easily  dialyzable  and  is  not  taken  out  of  its  liquid  form 
by  any  of  the  common  reactions  which  coagulate  and  pre- 
cipitate ordinary  albumens.  Every  one  is  familiar  with  the 
fact  that  most  common  albumens  will  coagulate  when 
heated,  and  that  the  albumen  in  milk  will  coagulate  when 
treated  with  an  acid.  This  latter  is  the  common  process  of 
curdling.  While  the  introduction  of  alkalies  or  strong 
mineral  salts  will  at  once  precipitate  these  albumens  in  the 
form  of  white  insoluble  flakes  it  does  not  precipitate  pep- 
tones. 

It  is  not  possible  to  get  pepsin  in  an  absolutely  pure 
form.  For  commercial  purposes,  however,  it  may  be 
secured  with  satisfactory  purity.  For  these  purposes  it  is 
extracted  from  the  gastric  mucous  membrane  of  various 
animals,  and  then  mixed  with  starch  or  sugar  of  milk  and 
placed  on  the  market.  For  laboratory  experiments  to  show 
artificial  gastric  digestion  the  pepsin  may  be  secured  by 
taking  the  gastric  mucous  membrane  of  an  animal,  cutting 
it  up  very  finely,  and  then  extracting  the  pepsin  from  it 
with  glycerine.  These  glycerine  extracts  if  properly  diluted 
and  acidulated,  readily  digest  proteids  subjected  to  their 
action. 


334  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

In  the  medical  field  pepsin  in  some  form  or  other  is  fre- 
quently given  to  supplement  the  lack  of  this  material  in  the 
stomach.  In  fact,  the  disease  called  by  the  too-general 
term  dyspepsia,  is,  as  the  name  indicates,  frequently  inter- 
preted as  a  lack  of  the  pepsin.  Dyspepsia  is,  however,  a 
pathological  condition  of  the  alimentary  canal  which  is 
much  more  frequently  not  connected  directly  with  the  ab- 
sence or  presence  of  the  pepsin,  but  is  due  to  bacterial  fer- 
mentation set  up  in  the  carbohydrates. 

b. — Hydrochloric  Acid.  Gastric  juice  contains  about 
two  parts  of  free  hydrochloric  acid  in  a  thousand.  This 
fact  is  somewhat  remarkable,  as  it  is  the  only  mineral  acid 
in  the  body  which  occurs  in  a  free  condition.  It  is  inter- 
esting to  note  in  this  connection  that  a  certain  mollusk  of  the 
genus  Dolium  secretes  a  salivary  juice  which  contains  beside 
the  free  hydrochloric  acid  free  sulphuric  acid.  Of  the  ex- 
act manner  in  which  this  acid  is  formed  in  the  stomach  we 
know  as  yet  nothing.  There  is  a  good  deal  of  evidence 
pointing  to  the  oxyntic  cells  of  the  stomach  as  the  seat 
of  the  production,  but  the  chemistry  of  it  is  still  missing. 
The  only  reasonable  explanation  is  that  some  of  the  neu- 
tral salts,  like  common  salt,  which  is  a  combination  of 
sodium  and  hydrochloric  acid,  are  split  into  the  free  acid 
which  then  passes  into  the  stomach,  and  the  alkaline  base 
which  passes  into  the  blood  and  which  may  account  for  the 
fact  that  the  blood  is  normally  alkaline  even  when  no  alka- 
line salts  are  found  in  the  food. 

c. — Rennet.  In  the  making  of  cheese  it  was  long  an 
observed  fact  that  sweet  milk  could  be  made  to  curdle 
quickly  and  effectively  by  adding  to  the  milk  a  piece  of  the 
mucous  membrane  of  a  calf's  stomach,  or  of  some  animal 
living  upon  a  milky  diet.  There  seems  to  be  in  the  mucous 
membrane  in  question  a  ferment  which  has  the  power  to 
coagulate  milk.  This  ferment  is  called  "rennet"  or 
remain.  It  has  not  been  possible  to  get  this  rennet  in  a 
pure  form,  and  so  its  composition  is  not  known.  It  is 


DIGESTION    AND    THE    DIGESTIVE   AGENTS.  335 

found  in  a  much  more  concentrated  form  in  the  stomachs 
of  sucking  animals,  for  which  reason  these  stomachs  are 
used  in  the  preparation  of  cheese,  but  in  diluted  and  weaker 
forms  it  maybe  extracted  from  the  stomachs  of  all  mammals. 
No  doubt  the  curdling  of  milk  in  the  adult  stomach  is 
largely  due  to  the  presence  of  the  acid  in  the  stomach ;  but 
it  can  be  shown  that  gastric  juice  may  be  perfectly  neutral 
and  still  retain  its  power  of  curdling  milk.  The  chemical 
nature  of  this  process  is  not  known.  Possibly  it  is  not  very 
unlike  the  coagulation  of  blood,  a  fact  which  seems  to  gain 
credence  in  the  observation  that  the  milk  will  not  clot  or 
curdle  unless  lime  salts  are  present.  The  action  of  the 
rennet,  however,  goes  no  further  than  the  curdling  of  the 
milk.  As  soon  as  this  is  effected  its  action  ceases,  and  by 
the  pepsin  the  milk  is  converted  into  soluble  peptones. 

The  mineral  salts  are  the  chlorides  and  phosphates  of 
potassium,  calcium,  magnesium  and  iron,  but  as  they  figure 
in  no  integral  way  in  gastric  digestion  we  are  not  specially 
concerned  with  them  here. 

GASTRIC   DIGESTION   OF   CARBOHYDRATES   AND 
HYDROCARBONS. 

Gastric  juice  exerts  no  digestive  action  upon  the 
starches.  The  starches  in  a  perfectly  unaltered  condition 
are  passed  into  the  intestine,  and  their  digestion  there 
turned  over  to  the  pancreas.  Nor  are  the  sugars  affected, 
although  there  would  be  no  special  reason  for  a  change  in 
sugars,  as  all  the  sugars  are  soluble  and  dialyzable  to  begin 
with.  Neither  are  the  fats  affected.  Bits  of  tallow,  lard 
or  butter  suffer  no  digestive  changes  in  the  stomach,  save 
that  by  the  general  mixing  of  the  stomach  they  are  broken 
up  into  small  bits.  However,  very  frequently  the  fats  are 
eaten  not  as  pure  fat,  but  in  the  form  of  droplets  of  fat  en- 
closed in  albuminous  coverings.  Thus  in  ordinary  milk  and 
cream,  the  butter  is  held  in  the  form  of  minute  droplets, 
each  surrounded  by  a  thin  albuminous  envelope.  To  get 
the  butter  in  a  pure  form  it  is  of  course  necessary  to  break 


336  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

these  envelopes  and  allow  the  contents  to  run  together,  a 
result  which  is  easily  brought  about  by  the  mechanical 
crushing-  of  these  envelopes  in  the  familiar  process  of 
churning.  It  might,  however,  be  brought  about  just  as 
easily  by  adding  bits  of  pepsin  and  acid  to  the  cream  and 
allowing  this  pepsin  to  digest  away  the  albuminous  cover- 
ings, and  so  permit  the  buttery  droplets  to  run  together. 

Such  a  condition  of  things  we  meet  with  in  the  stomach. 
Fats  taken  in  the  form  of  such  droplets,  as  in  milk  or  cream, 
have  their  albuminous  covering  digested  away  by  the  gas- 
tric juice,  and  the  fatty  contents  liberated.  Or  when  fatty 
meat  is  taken,  the  connective  tissue  covering  as  well  as  the 
coverings  of  the  fatty  cells  are  digested  away  and  the  con- 
tained fat  set  free.  But  this  action  is  clearly  an  action  on 
the  albumens  and  albuminoids,  and  has  really  nothing  to  do 
with  the  digestion  of  the  fats  themselves. 

Gastric  juice  will  digest  the  albuminoids.  Bits  of  white 
fibrous  tissue,  or  ordinary  connective  tissue  or  cartilage  are 
disintegrated  and  the  gelatine  extracted. 

SUMMARY. 

When  the  process  of  gastric  digestion,  after  a  period  of 
four  or  five  hours  comes  to  an  end,  we  find  the  following 
state  of  things: 

First.  The  change  from  the  starch  to  the  sugars  begun 
by  the  ptyalin  in  the  mouth  is  temporarily  arrested  in  the 
acid  juice  of  the  stomach. 

Second.  A  large  part  of  the  proteids  have  been  taken 
through  several  intermediate  stages  and  been  finally  changed 
into  dialyzable  peptones. 

Third.    Starches  have  in  no  wise  been  affected. 

Fourth.  Pure  fats  have  not  been  affected  at  all,  but  fats 
when  surrounded  with  albuminous  envelopes,  as  in  the  case 
of  milk  or  cream,  or  of  fat  meat,  have  had  these  albumin- 
ous coverings  digested  away,  and  been  thus  liberated. 

Fifth.    Sugars  have  not  been  acted  upon. 


DIGESTION    AND   THE    DIGESTIVE   AGENTS.  337 

Sixth.  The  milk  has  been  curdled  by  the  acid  of  the 
stomach  and  by  the  rennin,  and  more  or  less  fully  converted 
into  peptones  by  the  pepsin. 

Seventh.  A  number  of  mineral  salts  which  we  take  into 
the  body  daily,  as  ashy  ingredients  of  our  foods,  have  been 
dissolved  by  the  acid  of  the  stomach  and  so  enabled  to 
pass  into  the  blood.  In  this  way  much  of  the  mineral  mat- 
ter for  the  body,  which  would  be  perfectly  insoluble  in  water 
is  dissolved,  and  so  rendered  suitable  for  the  body's  pur- 
poses. With  the  gastric  contents  in  this  condition  the  py- 
loric  sphincter  from  time  to  time  relaxes,  and  the  now 
fairly  semi-liquid  food  is  passed  into  the  duodenum  to  be 
further  subjected  to  the  action  of  the  succeeding  digestive 
agents. 

The  explanation  why  the  stomach  does  not  digest  itself 
is  given  by  some  as  due  to  the  resistance  of  its  epithelial 
lining,  by  means  of  which  it  is  protected  from  the  digestive 
action  of  the  juice,  the  keratin  of  the  epithelium  cells  being 
indigestible.  Others  find  the  explanation  in  the  circulating 
alkaline  blood  through  the  walls,  by  means  of  which  the 
walls  themselves  can  never  become  acid,  and  so  never  sus- 
ceptible to  the  action  of  the  gastric  juice.  It  is  interesting 
to  note  that  ulcerations  of  the  mucous  membrane  become 
susceptible  to  self-digestion,  which  may  finally  lead  to  the 
formation  of  holes  through  the  gastric  wall. 

3. — The  Pancreatic  Juice.  Fresh  pancreatic  juice  is  a 
clear,  viscid,  alkaline,  rapidly  putrefying  liquid,  slightly 
heavier  than  water,  coagulating  completely  when  subjected 
to  boiling.  Its  composition  is  as  follows: 

First,  albumens.  Just  what  the  exact  nature  of  these 
albumens  is  has  not  yet  been  determined.  They  coagulate 
easily  upon  being  boiled.  Whether,  in  fact,  they  have  any 
digestive  action  at  all  is  still  questionable. 

Second,  several  ferments  or  enzymes.  These  enzymes 
are  trypsin,  amylopsin,  and  steapsin. 

Third,  a  number  of  mineral  salts,  mostly  sodium  salts. 

Fourth,  water. 
22 


338  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

About  ninety  per  cent,  of  the  pancreatic  juice  is  water. 
Dissolved  in  it  are  the  mineral  salts,  to  which  the  alkalinity 
of  this  juice  is  due,  for  unlike  the  gastric  juice,  the  ferments 
of  the  pancreatic  juice  can  act  in  an  alkaline  medium  only, 
and  not  in  an  acid  one.  The  pre-eminence  of  pancreatic 
juice  as  a  digestive  agent,  exceeding  very  much  that  of  the 
pepsin  or  ptyalin,  is  due  to  the  presence  of  the  three  fer- 
ments named,  trypsin  amylopsin  and  steapsin. 

Trypsin.  Trypsin  is  a  very  powerful  ferment  changing 
with  great  energy  proteids  into  peptones.  It  is  this  ferment 
which  acts  iipon  all  those  proteids  left  unacted  upon  by  the 
stomach,  and  upon  all  of  the  intermediate  stages  left  incom- 
plete by  the  pepsin.  Here,  too,  the  change  from  the  pro- 
teids to  the  peptones  is  not  a  simple  and  direct  one,  there 
being  a  number  of  intervening  stages  called  here,  also,  pro- 
teoses,  the  final  resulting  stage,  however,  being  peptone  in 
no  essential  way  distinguishable  from  the  peptone  made  by 
the  stomach.  The  powerful  digestive  action  of  trypsin  is 
shown  in  the  fact  that  some  of  "the  peptone  is  disintegrated 
still  further  into  two  substances  called  leudn  and  tyrosin, 
substances  which  the  chemist  may  readily  detect  where  pan- 
creatic digestion  is  going  on,  but  the  physiological  signifi- 
cance of  which  we  are  at  present  not  at  all  able  to  under- 
stand. The  peptones  are,  of  course,  the  source  of  the  ni- 
trogenous foods  of  the  body,  but  why  some  of  the  peptones 
should  be  broken  up,  that  is,  digested  still  further  into 
bodies  like  leucin  and  tyrosin,  bodies  which  seem  to  play 
no  part  as  foods,  is  not  at  all  clear.  The  trypsin  is  also  able 
to  digest  any  albuminoids  which  may  have  escaped  diges- 
tion in  the  stomach. 

Amylopsin.  Amylopsin  is  a  ferment  of  the  pancreatic 
juice  identical  with  the  ptyalin  of  the  saliva,  and  like  this 
ptyalin  possesses  the  property  of  changing  starch  into  mal- 
tose. The  pancreas  is  called  by  the  Germans  the  "Ab- 
dominal Salivary  Gland,"  no  doubt  because  of  the  identity 
of  its  action  on  the  starches,  with  the  salivary  glands.  The 


DIGESTION    AND    THE    DIGESTIVE    AGENTS.  339 

starches  which  are  left  entirely  unacted  upon  in  the  stomach, 
are  now  subjected  anew  to  ferments.  The  ptyalin  of  the 
saliva  continues  its  action,  while  the  amylopsin  added  from 
the  pancreatic  juice  soon  completes  the  digestion  of  the 
starches  and  effects  their  entire  change  into  soluble  mal- 
tose. There  is  no  good  reason  for  calling  the  ptyalin  of  the 
pancreatic  juice  by  a  new  name  unless  it  be  that  the  term 
"amylopsin"  indicate  the  source  from  which  the  ptyalin  is 
derived. 

Steapsin.  Steapsin  is  a  ferment  of  the  pancreatic  juice 
which  has  the  property  of  splitting  fats  into  a  fatty  acid  and 
glycerine.  The  chemical  nature  of  this  change  is  the  same 
as  that  of  ptyalin.  Under  the  action  of  the  steapsin  the  fat 
is  made  to  combine  with  more  water  and  the  resulting 
molecule  is  then  split  up  into  glycerine  and  a  free  fatty  acid. 
It  has  not  been  possible  to  isolate  this  steapsin,  and  so  we 
know  at  present  nothing  about  its  chemical  nature.  The 
splitting  up  of  fats  into  a  fatty  acid  and  glycerine  is,  how- 
ever, a  very  common  occurrence  and  familiar  to  every  one. 
When  butter  becomes  old,  it  acquires  an  offensive,  rank 
odor.  This  is  due  to  the  fact  that  the  butter,  which  is  a 
pure  fat,  has  been  split,  in  this  case  by  an  organic  ferment, 
into  an  acid  called  butyric  acid,  and  glycerine.  It  is  the 
butyric  acid  which  has  the  disagreeable  odor.  The  same 
thing  is  true  of  other  fats.  Exposed  for  a  long  time  they 
become,  as  we  say,  strong  and  rank,  the  explanation  of 
which  is  found  in  the  fact  that  these  pure  fats  have  been 
split  into  a  fatty  acid,  hence  their  odor,  and  glycerine. 
These  fatty  acids  may  be  made  to  combine  easily  with  some 
form  of  alkali  and  so  soap  produced.  Soap  is,  in  fact, 
nothing  but  the  combination  of  a  fatty  acid  with  some  suit- 
able alkali.  In  the  once  very  common  manufacture  of 
household  soap,  the  rank  fats  were  boiled  in  a  kettle  with 
some  form  of  lye,  the  resulting  combination  being  soap. 

The  physiological  value  of  the  ferment,  steapsin,  is 
found  not  immediately  in  the  fact  that  it  splits  these  fats  up 
into  glycerine  and  fatty  acid,  but  in  the  succeeding  fact,  that 


340  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  fatty  acids  so  produced  in  the  intestine,  unite  with  some 
of  the  alkaline  ingredients  present  and  form  soap.  It  can 
be  easily  shown  in  a  chemical  laboratory  that  the  formation 
of  soap  is  practically  impossible  when  a  perfectly  pure  fat 
is  used.  Traces  of  a  fatty  acid  must  be  present  to  help  the 
process  along.  In  the  intestine  this  fatty  acid  is  produced 
by  the  steapsin  and  so  the  formation  of  soap  rendered  pos- 
sible and  simple. 

The  question  then  at  once  arises,  what  the  physiological 
value  of  soap  is  in  the  intestine.  In  the  first  place,  soap  is 
soluble  and  dialyzable,  while  ordinary  fat  is  not  very  dialyz- 
able,  and  so  if  the  fats  are  changed  into  soap  it  will  make 
quite  easy  the  transfer  of  these  substances  into  the  blood. 
The  same  is  true  of  glycerine  also,  which  is  always  formed 
when  the  fats  split  up  into  a  fatty  acid. 

The  main  purpose,  however,  of  the  soap  is  probably  to 
aid  in  the  emulsification  of  the  remaining  fats.  It  was 
pointed  out  in  discussing  the  action  of  the  gastric  juice  on 
fats  that  all  the  fats  were  liberated.  In  the  intestine  they 
are  prepared  for  absorption.  A  small  per  cent,  of  them,  as 
just  indicated,  is  changed  into  fatty  acid,  and  then  into 
soap.  The  rest  is  emulsified.  An  emulsification  of  an  oil 
or  fat  is  effected  when  the  oil  in  question  is  shaken  up  very 
thoroughly  with  some  liquid,  so  that  the  two  seem  to  have 
been  intimately  mixed  and  the  fat  is  prevented  from  run- 
ning together  by  being  suspended  in  tiny  droplets  sur- 
rounded by  a  thin  envelope  to  prevent  them  reuniting. 
Thus,  cream  is  an  emulsion  of  butter,  the  tiny  particles  of 
butter  being  surrounded  by  an  albuminous  covering  and  so 
prevented  from  running  together.  Lather  is  an  emulsion 
of  air  and  soap-suds.  The  significance  of  the  emulsifica- 
tion of  the  fats  lies  in  the  fact  that  the  bits  of  fat  in  the  in- 
testine are  separated  into  very  tiny  particles  small  enough 
to  pass  through  the  walls  of  the  alimentary  canal  in  a 
manner  to  be  described  in  the  following  chapter.  In  large 
chunks  or  bits  this  would  be  impossible,  but  reduced  to 


DIGESTION   AND   THE   DIGESTIVE   AGENTS.  341 

tiniest  globules  the  absorbing  cells  of  the  intestine  are  able 
to  manage  them  properly. 

In  the  emulsion  of  these  fats  the  soap  formed  in  the  in- 
testine seems  to  figure  directly.  Probably  the  tiny  little 
droplets  of  fat  are  surrounded  by  thin  envelopes  of  soap  and 
so  prevented  from  reuniting.  That  soap  is  pre-eminently 
fitted  in  making  an  emulsion  is  evident  as  soon  as  we  think 
of  soap-suds  and  lather.  We  have,  therefore,  to  picture  to 
ourselves  the  way  in  which  the  fat  is  acted  upon  about  as 
follows:  The  liberated  fats  of  the  stomach  reach  the  in- 
testine, meet  some  of  the  steapsin  ferment,  and  are  then 
partly  split  into  a  fatty  acid  and  glycerine.  The  fatty  acid 
at  once  unites  with  some  alkaline  ingredient  of  the  pan- 
creatic juice  or  bile  and  soap  is  formed.  This  soap  by 
means  of  the  peristaltic  motions  of  the  intestine  is  shaken 
up  with  the  remaining  fats  and  emulsifies  them,  so  getting 
them  ready  for  absorption.  That  some  of  the  fats  in  the 
form  of  soap,  finally  reach  the  blood,  is  probable,  but  the 
physiological  value  of  this  soap  is  in  its  emulsifying  action 
upon  the  remaining  and  larger  portion  of  the  fats. 

Summary.  What,  then,  is  the  final  state  of  things 
after  the  process  of  pancreatic  digestion  has  continued  for 
several  hours? 

Of  course  while  the  pancreatic  digestion  has  been  going 
on  the  bile  has  been  poured  into  the  intestine  and  has  pro- 
duced some  effects,  and  the  intestinal  juice  has  also  been 
acting.  But  leaving  this  out  of  consideration  for  the  pres- 
ent the  final  state  of  things  is  about  as  follows : 

First:  All  the  proteids  which  the  stomach  has  left  un- 
touched and  all  those  proteids  which  the  stomach  has 
only  partially  changed  into  peptones,  have  been  completely 
changed  into  peptones  by  the  trypsin. 

Second:  Any  albuminoids  that  may  have  escaped  di- 
gestion in  the  stomach  are  dissolved  and  the  gelatine  ex- 
tracted. 


342  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

Third:  All  the  starches  are  finally  changed  into  maltose 
by  the  renewed  action  of  the  ptyalin  of  the  saliva,  but 
mainly  by  that  of  the  amylopsin  ferment  of  the  pancreas. 

Fourth:  The  fats  have  been  doubly  affected.  A  small 
part  has  been  saponified,  that  is,  made  into  soap  by  the 
steapsin,  and  the  remainder  has  been  emulsified.  Sugars 
have  been  left  untouched.  It  will  be  seen,  therefore,  that 
at  this  stage  of  digestion  all  the  proteids,  all  the  fats,  all 
the  starches  are  ready  for  absorption.  The  sugars  alone 
have  escaped  any  action. 

4. — The  Bile.  The  liver  plays  but  a  very  small  part  in 
the  process  of  digestion,  and  the  bile  which  it  pours  into 
the  duodenum  must  not  be  classed  in  importance  along  with 
the  digestive  agents  so  far  considered.  The  liver  is  an  ex- 
ceedingly important  organ  when  the  phenomena  of  nutri- 
tion and  metabolism  in  the  body  are  considered,  but  plays 
a  minor  role  in  digestion.  In  fact,  bile  is  largely  an  excre- 
tory product.  It  digests  nothing  itself,  although  incidentally 
it  does  serve  several  digestive  purposes.  Human  bile  is  of 
a  golden  color,  exceedingly  bitter,  neutral  in  its  re-action, 
and  emitting  a  peculiar  characteristic  odor.  It  is  a  little 
heavier  than  water.  When  the  bile  is  taken  from  the  gall- 
bladder it  contains  a  mucin-like  substance  which  was  added 
to  it  in  its  passage  through  the  bile-ducts  and  in  its  stay  in 
the  gall-bladder.  This  was  formerly  designated  as  ordinary 
mucin,  but  its  re-actions  are  not  those  of  ordinary  mucin, 
and  it  is  probably  a  slightly  different  product.  However, 
in  a  general  way  we  may  still  speak  of  it  as  mucin.  While 
the  color  is  usually  a  golden  yellow  it  changes  its  color  so 
readily  as  to  appear  sometimes  a  greenish  yellow,  some- 
times a  greenish  brown,  still  other  times  pure  green  or 
brown.  These  changes  in  color  are  brought  about  by  dif- 
ferent degrees  of  oxidation  of  the  bile  pigments. 

The  quantity  of  bile  secreted  during  a  day  for  average 
persons  is  from  600  to  900  cubic  centimeters.  In  animals 
which  have  no  gall-bladder  the  bile  is  poured  into  the  in- 
testine in  a  continuous  stream,  but  in  those  possessing  a 


DIGESTION    AND    THE    DIGESTIVE    AGENTS.  343 

gall-bladder  the  secretion  is  allowed  to  accumulate  in  that, 
from  which  in  turn  it  is  ejected  in  spurts  at  stated  periods 
into  the  duodenum.  The  average  composition  of  bile  in- 
cludes the  following  substances  in  1,000  parts: 

Water  about  900  parts, 
Mucin  about  25  parts, 
Bile  salts  about  30  parts, 
Cholesterin  about  2  parts, 
Mineral  salts  about  10  parts, 

Also  traces  of  soap,  fats,  and  lecithin.  In  addition  to  these 
there  are  traces  of  bile  pigments,  to  which  the  color  of  the 
bile  is  due.  The  large  amount  of  water  serves,  of  course, 
as  the  fluid  medium  in  which  all  the  other  substances  are 
dissolved  and  by  which  they  are  carried. 

The  Bile  Salts.  The  most  important  constituents  of  the 
bile  are  the  bile  salts.  These  are  the  sodium  salts  of  two 
peculiar  acids  called  glychocholic  acid  and  taurocholic  acid. 
It  would  be  out  of  place  here  to  go  into  the  chemistry  of 
these  organic  acids.  It  may,  however,  be  of  interest  to  call 
attention  to  the  point  that  the  taurocholic  acid  contains 
sulphur.  These  two  acids  are  not  found  in  the  blood,  but 
are  made  by  the  cells  of  the  liver  and  by  these  poured  into 
the  bile-ducts.  They  are  probably  substances  which  have 
resulted  from  the  breaking  down  of  some  proteid  or  albu- 
minoid substance  in  the  process  of  metabolism,  and  are 
primarily  intended  for  removal  from  the  body.  It  is  inter- 
esting, however,  to  note  that  these  bile  salts  are  re-digested 
in  the  intestine,  and  are  almost  wholly  re -absorbed  into 
the  system.  These  bile  salts  have  some  important  func- 
tions; in  fact,  they  are  considered  indispensable,  and  are 
treated  by  some  physiologists  as  by  no  means  mere  excre- 
tions, but  special  secretions  intended  for  specific  purposes. 
In  the  first  place  these  bile  salts  hold  in  solution  the  cho- 
lesterin  of  the  bile.  Cholesterin  is  insoluble  in  the  bile  as 
soon  as  the  bile  salts  are  removed.  It  is  a  non-nitrogenous 
substance  very  widely  distributed  in  the  body,  being  found 
especially  abundant  in  the  white  matter  of  nerve  tissues.  In 


344  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

small  amounts,  however,  it  is  found  in  all  animal  and  plant 
cells.  This  cholesterin  is,  therefore,  probably  not  formed 
in  the  liver,  but  is  merely  eliminated  by  the  liver  cells  from 
the  blood,  and  poured  into  the  bile  secretion  to  be  removed 
from  the  body.  As  far  as  we  know  now  it  is  a  pure  excre- 
tion, the  accumulation  of  which  in  the  blood  would  prove 
dangerous.  It  is  sometimes  precipitated  in  the  bile-ducts 
or  gall-bladder  and  so  gives  rise  to  the  formation  of  gall 
stones,  which  may  in  many  cases  consist  of  pure  cholesterin, 
the  removal  of  which  from  the  gall-bladder  or  bile-ducts 
is  frequently  a  matter  of  the  severest  pain,  and  oftentimes 
results  fatally.  In  the  second  place  these  bile  acids  seem 
to  facilitate  the  absorption  of  fats  from  the  intestine,  and  to 
help  materially  in  the  emulsion  of  the  fats,  a  point  to  be 
discussed  later.  The  exceedingly  bitter  taste  of  bile  is  due 
to  these  organic  bile  salts. 

The  Bile  Pigments.  The  bile  owes  its  color  to  the  pres- 
ence of  small  amounts  of  substances  called  bile  pigments. 
These  pigments,  according  to  the  animals  from  which  they 
are  taken,  are  of  two  kinds,  the  golden  bilirubin  or  the 
greenish  biliverdin.  The  bilirubin  is  present  in  fresh  human 
bile  and  occurs  normally  in  the  bile  of  most  carnivora.  On 
the  other  hand  the  bile  pigments  in  the  case  of  most  herbi- 
vorous animals  is  the  greenish  biliverdin.  Biliverdin  and 
bilirubin  are  practically  the  same,  one  being  only  a  slight 
oxidation  product  of  the  other,  and  it  is  very  easy  by  this 
means  to  change  one  into  the  other.  This  fact  is  made  use 
of  in  detecting  the  presence  of  bile  pigments.  If  to  some 
human  bile  in  a  test-tube  a  little  fuming  nitric  acid  be 
added,  the  acid  being  heavier  will  sink  to  the  bottom,  the 
bile  being  in  contact  with  it  above.  At  this  point  of  con- 
tact the  bilirubin  undergoes  a  succession  of  color  changes, 
through  green,  blue  and  violet,  to  yellow.  This  play  of 
colors  is  due  to  the  successive  stages  of  oxidation  of  the 
bile  pigments.  The  bilirubin  is  in  the  first  stage  changed 
to  green,  a  change  due  to  the  formation  of  biliverdin.  In 


DIGESTION   AND   THE    DIGESTIVE    AGENTS.  345 

such  a  test  tube  the  colors  will  arrange  themselves  one 
above  the  other  in  the  order  indicated,  the  most  advanced 
stage  of  oxidation  being  of  course  next  to  the  nitric  acid, 
the  least  advanced  stage  of  oxidation  on  top  of  the  liquid. 
This  characteristic  re-action  for  the  detection  of  bile  pig- 
ments, familiar  to  all  physiological  laboratories,  is  called 
"Gmelin's  re-action. "  It  is  a  very  sensitive  one,  and  by 
means  of  it  the  presence  of  bile  pigments  has  been  detected 
in  other  liquids  of  the  body,  as  for  instance,  the  secretion 
from  the  kidneys.  The  bile  pigments  are  of  especial  inter- 
est, because  it  is  fairly  well  established  that  they  are  derived 
from  haemoglobin.  When  the  red  corpuscles  break  down 
in  the  circulation  or  disintegrate  in  the  spleen  or  liver,  the 
colored  haemoglobin  is  sent  to  the  liver,  and  by  the  liver 
cells  is  converted  into  bilirubin  or  biliverdin.  Haemoglobin 
contains  iron,  but  bilirubin  and  biliverdin  are  iron -free. 
This  shows  that  the  iron  in  the  haemoglobin  must  be  re- 
tained in  the  liver,  and  possibly  dropped  back  into  the  blood 
and  sent  to  the  marrow  of  the  bones,  to  be  used  anew  in 
the  formation  of  fresh  haemoglobin.  The  amount,  there- 
fore, of  bilirubin  or  biliverdin  eliminated  in  the  bile  would 
give  us  a  clue  to  the  rapidity  of  corpuscular  disintegra- 
tion. 

Bile  is  practically  a  watery  solution  of  certain  mineral 
salts  which  holds  in  solution  goodly  quantities  of  the  or- 
ganic bile  salts.  These  organic  bile  salts  hold  in  solution 
the  cholesterin  of  the  bile,  and  finally  the  bile  pigments  to 
which  the  color  is  due.  In  addition  to  these  main  constitu- 
ents there  are  found  in  bile  traces  of  fats  and  soaps,  and  a 
peculiar  substance  called  lecithin,  which  is  interesting  be- 
cause it  is  always  found  in  nervous  tissues  and  characterized 
by  containing  phosphorus.  It  is  no  doubt  a  mere  disinte- 
gration product  resulting  from  the  activity  of  these  tissues 
and  sent  to  the  bile  merely  to  be  removed  as  a  waste 
product. 

The  reason  for  the  presence  of  the  fats  and  soaps  in  the 
bile  is  still  missing. 


346  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

The  General  Physiology  of  Bile.  Our  knowledge  of 
the  physiological  value  of  bile  still  leaves  much  to  be  de- 
sired. Here  more  than  with  any  other  of  the  digestive 
agents  our  knowledge  is  fragmentary,  and  there  is  at  present 
still  no  unanimity  among  leading  physiologists  as  to  the  role 
which  it  plays.  It  seems  probable,  however,  that  the  intro- 
duction of  bile  into  the  duodenum  accomplishes  the  follow- 
ing results : 

First.  Bile  is  a  slightly  alkaline  liquid,  and  as  such 
poured  in  large  quantities  into  the  intestine  it  overcomes 
and  destroys  the  acidity  of  the  food  as  it  comes  from  the 
stomach,  and  so  prepares  the  material  for  the  pancreatic 
digestion,  which  can  only  occur  in  an  alkaline  medium. 

Second.  Bile  possesses  to  a  considerable  extent  the 
property  of  emulsifying  fats,  and  so  materially  assists 
the  pancreatic  juice  in  this  function.  This  property  of 
the  bile  is  derived  from  the  organic  bile  salts.  It  has 
been  stated  by  some  physiologists  that  bile  has  the  prop- 
erty of  splitting  up  pure  fats  into  fatty  acids,  and  so  to  as- 
sist the  steapsin  of  the  pancreatic  juice  in  the  formation  of 
soaps.  The  emulsifying  power  of  bile  can  be  readily  dem- 
onstrated by  simply  shaking  up  bile  and  oil,  the  result  of 
which  is  a  fairly  stable  emulsion. 

Third.  Bile  is  a  mild  stimulant  and  so  starts  the  peris- 
taltic actions  of  the  intestine.  It  has  been  observed  that  a 
sudden  gush  of  bile  into  the  intestines  will  cause  a  peristal- 
tic contraction  to  begin  at  that  point  and  to  creep  slowly 
downward.  It  would,  so  to  speak,  be  nature's  laxative  and 
the  sluggishness  of  the  intestines  which  follows  the  with- 
holding of  bile  from  them,  as  in  various  cases  of  bilious- 
ness, may  be  partly  explained  in  this  way.  This  stimulat- 
ing effect  of  the  bile  is  again  due  to  the  glychocholic  and 
taurocholic  acid  salts. 

Fourth.  It  is  asserted  by  some  physiologists,  but  stren- 
uously denied  by  others,  that  bile  helps  in  the  absorption 
of  fats.  It  was  first  stated  that  an  animal  membrane  moist- 
ened with  bile  would  allow  fats  to  traverse  it  more  easily, 


DIGESTION    AND    THE    DIGESTIVE   AGENTS.  347 

but  its  validity  is  questioned.  Just  how  it  aids  in  the  ab- 
sorption of  fats  can  not  be  told.  The  fact,  however,  remains 
that  in  an  animal  in  which  none  of  the  bile  is  allowed  to 
reach  the  intestine,  which  may  be  done  easily  by  making 
a  biliary  fistula,  the  fat  is  not  so  readily  absorbed  from  the 
intestine  but  accumulates  there,  and  it  may  in  large  quan- 
tities be  actually  lost  from  the  body.  By  turning  the  stream 
of  bile  back  into  the  intestine  and  renewing  the  feeding  of 
fats,  at  once  larger  quantities  of  the  fats  are  absorbed  and 
practically  none  are  passed  out. 

We  know  that  the  absorption  of  fat  is  not  a  physical 
process,  like  the  dialysis  of  sugar  through  the  membrane, 
but  is  a  physiological  process  in  which  the  epithelial  cells 
of  the  intestines  actively  pick  up  the  fat,  and  it  is  probable 
that  the  helpful  action  of  the  bile  in  the  absorption  of  fats 
is  due  to  the  direct  stimulus  which  it  exerts  upon  the  epi- 
thelial cells.  A  stimulus  possibly  not  unlike  the  one  which 
it  exerts  upon  the  muscles  of  the  intestine  in  arousing  them 
to  greater  peristaltic  activity. 

Fifth.  Bile  is  to  a  slight  extent  antiseptic,  that  is,  it 
destroys,  or  more  properly,  retards  putrefying  changes. 
Such  an  antiseptic  function  has  been  assigned  to  it  in  the 
intestine.  But  before  calling  attention  to  this  antiseptic  in- 
fluence it  will  be  desirable  to  explain  more  in  detail  the 
reasons  for  the  putrefying  changes  which  occur  here.  Putre- 
faction is  a  process  of  disintegration,  a  kind  of  fermenta- 
tion caused  by  bacteria.  Such  bacteria,  however,  are  not 
dangerous  ones;  many  are  not  only  harmless,  but  actually 
helpful.  Such  helpful  bacteria  live  in  untold  numbers 
normally  and  regularly  in  the  human  intestine.  Here  in 
the  nutritious  contents  of  the  intestine  they  induce  putre- 
factive changes,  the  important  result  of  which  is  a  soften- 
ing and  partial  disintegration  of  the  food.  This  softening 
and  partial  disintegration  no  doubt  aids  materially  in  their 
digestion,  and  without  this  disintegrating  bacterial  influence 
the  efficiency  of  the  digestive  changes  would  be  very  ma- 
terially impaired.  Digestion  itself  is  a  sort  of  disintegra- 


348  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

tion,  a  putrefying  process,  resulting  not  only  in  softening 
but  actually  in  liquifying  foods.  It  is  customary  in  some 
portions  of  the  globe  to  submit  meats  to  a  partial  decompo- 
sition with  a  view  of  increasing  its  digestibility,  and  it  is  a 
common  procedure  in  the  manufacture  of  certain  forms  of 
cheese  to  allow  them  to  proceed  very  far  along  in  the  pro- 
cess of  decay  in  order  to  render  them  more  digestible  (some 
say  palatable) .  Similar  processes  are  constantly  at  work  in 
the  intestine,  and  so  in  a  very  short  time,  acted  upon  by 
untold  numbers  of  these  bacteria,  putrefactive  changes  en- 
sue and  the  food  is  hurried  down  the  process  of  disintegra- 
tion, and  by  the  digestion  finally  turned  into  the  proper 
dialyzable  form.  But  however  desirable  such  a  softening  may 
be  it  is  absolutely  necessary  that  this  decay  do  not  go  be- 
yond a  certain  stage.  If  it  does,  the  food  entirely  disinte- 
grates and  ceases  to  have  any  nutritive  value  whatever. 
The  point,  therefore,  is  to  so  regulate  and  control  these 
putrefactive  changes  that  they  shall  not  endanger  the  nu- 
tritive value  of  the  foods,  but  shall  stop  at  the  point  where 
the  needs  of  digestion  are  accomplished.  It  is  believed 
that  the  bile  exerts  such  an  influence.  Thrown  into  the  in- 
testine in  large  amounts  it  acts  as  a  slight  antiseptic,  check- 
ing, and  so  preventing  an  undue  putrefaction.  It  is  an  ob- 
served fact  that  in  animals  whose  bile  is  not  allowed  to  flow 
into  the  intestine  the  decaying  influences  are  much  greater 
and  putrefaction  is  excessive. 

5. — The  Intestinal  Juice.  As  described  in  the  chapter 
on  the  anatomy  of  the  digestive  system,  the  mucous  mem- 
brane of  the  small  intestine  contains  innumerable  little 
glands  called  the  crypts  of  L,ieberktihn,  the  secretion  from 
which  is  called  the  intestinal  secretion  or  succus  entericus. 
The  glands  of  Brunner  play  no  part  in  this  secretion.  They 
are,  as  was  pointed  out,  merely  escaped  peptic  glands,  and 
so  have  no  physiological  value  in  the  place  where  they  are 
found.  On  account  of  the  scantiness  of  the  intestinal  se- 
cretion, it  is  exceedingly  difficult  to  get  this  fluid  in  even 


DIGESTION   AND    THE    DIGESTIVE   AGENTS.  349 

practical  purity.  The  best  success  in  obtaining  it,  is  made 
by  an  operation  called  a  Thiry  fistula,  which  consists  in 
cutting  out  from  the  course  of  the  intestine  a  loop,  and  then 
sewing  the  cut  ends  together  again.  In  that  way  the  food 
is  again  enabled  to  pass  uninterruptedly  along  the  intestine, 
save  that  the  intestine  has  been  shortened  by  the  loop  re- 
moved. The  two  cut  ends  of  this  loop  are  then  sewed  into 
the  abdominal  wall  so  as  to  connect  with  the  exterior.  The 
nerves  and  blood  vessels  of  this  cut  loop  are  left  untouched, 
and  so  when  food  passes  along  the  intestine,  secretion  is 
also  induced  in  this  separated  piece.  This  secretion  is  then 
collected  and  studied. 

Such  a  fluid  is  light  yellow  and  strongly  alkaline.  It 
possesses  traces  of  albumin  and  is  a  little  heavier  than 
water.  The  alkalinity  of  this  solution  is  due  to  the  pres- 
ence of  a  relatively  large  amount  of  sodium  carbonate,  but 
the  general  chemical  constitution  further  than  that  is  not 
known.  In  spite  of  statements  by  some  physiologists  to 
the  contrary,  there  is  no  satisfactory  evidence  that  the  in- 
testinal juice  exerts  any  action  whatever  upon  proteids  or 
fats.  Upon  starches  it  has  a  slight  effect.  It  contains  a 
ferment  much  like  the  amylopsin  of  the  pancreas  which 
changes  starch  into  sugar.  However,  on  account  of  the 
scantiness  of  the  intestinal  juice  this  figures  very  little  in 
ordinary  digestion.  The  important  use  of  the  intestinal 
juice  seems,  however,  to  be  its  action  upon  the  sugars.  It 
contains  a  ferment  capable  of  converting  cane  sugar,  mal- 
tose and  lactose  into  ordinary  glucose  or  grape  sugar.  The 
sugars  which  occur  regularly  in  our  diet  are  ordinary  cane 
sugar  (the  sugar  of  commerce) ,  lactose  (the  sugar  in  sweet 
milk),  and  maltose,  the  sugar  into  which  the  starches 
eaten  have  been  changed  by  the  ptyalin  and  the  amylopsin. 
None  of  these  sugars  are,  however,  found  in  the  blood. 
The  sugar  in  the  blood  is  glucose  or  grape  sugar,  and  it 
was  long  a  question  just  how  the  sugars  of  the  diet  were 
changed  into  the  sugar  of  the  blood.  This  change  occurs 
in  the  wall  of  the  intestine  under  the  action  of  the  intestinal 


350  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

juice.  It  is  desirable  to  point  out  again  that  this  change  of 
the  sugars  does  not  occur  in  the  contents  of  the  intestine. 
The  intestinal  juice  is  too  scanty  to  have  much  effect  there, 
but  occurs  while  the  sugars,  which  are  quite  dialyzable,  are 
in  the  act  of  passing  through  the  intestinal  wall.  Here  in 
the  mucous  membrane  moistened  with  the  intestinal  juice, 
cane  sugar,  maltose  and  lactose  are  changed  into  glucose, 
and  in  that  form  all  the  carbohydrates  eaten  reach  the 
blood. 

GENERAL  SUMMARY. 

First.  The  proteids  are  not  affected  by  the  saliva.  By 
the  gastric  juice  they  are  more  or  less  completely  changed 
into  peptones,  and  by  the  pancreatic  juice  the  change  from 
proteids  into  peptones  is  made  complete,  save  that  in  the 
pancreatic  digestion  some  of  the  peptones  are  digested  still 
further  into  compounds  called  leucin  and  tyrosin. 

Second.  The  albuminoids  are  not  affected  by  the  saliva 
but  digested  by  the  gastric  juice,  and  the  digestion  when 
incomplete  completed  by  the  pancreatic  juice. 

Third.  The  starches  are  acted  upon  by  the  ptyalin  of 
the  saliva  and  partially  changed  into  maltose.  In  the 
stomach  all  action  upon  the  carbohydrates  is  suspended. 
In  the  intestine  the  ptyalin  renews  its  action,  but  is  aided 
by  the  amylopsin  of  the  pancreatic  juice  and  so  all  the 
starches  are  changed  into  maltose.  This  maltose,  then, 
together  with  the  cane  sugar  taken  in  the  food  and  the  lac- 
tose from  the  milk,  is  changed  by  the  intestinal  juice  into 
glucose  or  grape  sugar,  in  its  passage  through  the  walls. 

Fourth.  The  fats  are  not  acted  upon  by  the  saliva  and 
are  not  directly  affected  by  the  gastric  juice  either  except 
to  be  liberated  when  surrounded  with  albuminous  envel- 
opes, but  in  the  intestines  they  are  saponified  by  the  steap- 
sin  and  emulsified  by  the  soap  so  produced,  and  by  the 
bile. 

Fifth.  A  number  of  mineral  substances  insoluble  in 
water  are  dissolved  in  the  free  hydrochloric  acid  of  the 
stomach,  and  in  solution  reach  the  blood.  At  the  end  of 


DIGESTION   AND   THE   DIGESTIVE   AGENTS.  351 

the  process  of  digestion,  then,  we  have  these  resulting  com- 
pounds: First,  peptones;  second,  gelatine;  third,  glucose; 
fourth,  soaps  and  emulsified  fats.  We  have  now  to  con- 
sider in  what  manner  and  by  what  routes  these  final  pro- 
ducts of  digestion  reach  the  tissues  of  the  body. 


CHAPTER  XV. 


ABSORPTION  AND  THE  ROUTES  OF  FOOD. 

In  the  preceding  chapter  the  various  changes  were  fol- 
lowed by  which  the  undigested  foods  were  transformed  into 
substances  which  were  able  to  dialyze  through  the  alimen- 
tary wall  into  the  blood.  It  was  until  recently  believed 
that  the  absorption  of  all  of  the  foods,  with  the  possible  ex- 
ception of  fat,  was  a  mere  physical  process,  and  therefore 
animal  membranes  were  taken  to  establish  experimentally 
the  details  of  the  process.  More  recent  work  in  this  field 
proves  conclusively  that  we  have  to  do  here  with  something 
more  than  mere  physical  osmosis;  something  more  than 
mere  filtration.  We  have  to  do  here  with  living  epithelium 
cells,  which  in  a  very  active  way,  and  according  to  physio- 
logical laws  of  their  own,  materially  modify  the  simple 
physical  process. 

No  doubt  much  of  the  food  employed  does  pass  into  the 
blood  by  simple  physical  osmosis,  but  there  is  reason  to  be- 
lieve that  by  far  the  largest  proportion  of  the  food  absorbed 
is  transferred  into  the  system  in  consequence  of  the  active 
participation  of  the  living  epithelium  cells.  This  will  ex- 
plain why  a  dead  piece  of  intestine  has  lost  to  so  great  an 
extent  its  power  to  absorb. 

The  exact  way  in  which  these  living  cells  participate  in 
this  absorption  we  do  not  at  present  understand.  Simple 
physical  osmosis,  however,  may  be  easily  studied  on  dead 
animal  membranes.  If,  for  instance,  such  a  membrane  be 
placed  between  two  liquids  of  different  composition,  currents 
are  at  once  set  up  through  it  tending  to  equalize  the  com- 
position of  the  two  fluids,  the  strength  of  the  currents  de- 
pending upon  the  dialyzing  power  of  the  substances  dis- 
solved. Thus,  if  on  one  side  of  such  a  membrame  a  solu- 
tion of  salt  be  placed,-  and  on  the  other  side  a  solution  of 


ABSORPTION    AND    THE    ROUTES    OF    FOOD.  353 

sugar,  the  salt  will  tend  to  flow  toward  the  sugar  side  and 
the  sugar  toward  the  salt  side.  These  currents  will  con- 
tinue until  finally  the  composition  of  both  sides  is  the  same. 
The  ease,  however,  with  which  substances  pass  through 
membranes  varies  materially  and  is  probably  not  the  same 
with  any  two  substances.  Some,  like  the  soluble  mineral 
salts  and  sugars,  dialyze  easily,  while  others,  such  as  albu- 
mins, dialyze  with  great  difficulty.  But  not  only  do  sub- 
stances in  solution  pass  through  the  membrane,  but  the 
water  itself  seeps  through.  Thus,  if  a  solution  of  salt  be 
placed  on  one  side  of  an  animal  membrane  and  pure  water 
on  the  other,  not  only  will  the  salt  seep  across,  but  the 
water  from  the  pure  side  will  flow  toward  the  salt  side,  and 
in  this  way  by  the  dilution  of  the  salt  solution  an  equilibrium 
is  finally  established. 

An  example  of  osmosis  can  be  readily  illustrated  on  an 
ordinary  hen's  egg.  Every  one  is  familiar  with  the  fact 
that  a  hen's  egg  which  has  been  kept  a  day  or  two  has  at 
its  blunt  end  an  air  space.  This  space  is  enclosed  between 
the  two  walls  of  the  shell  membrane.  If,  now,  the  shell 
and  that  part  of  the  membrane  adhering  to  it  be  removed 
from  above  the  air  space,  and  the  egg  then  partially  immersed 
in  water,  osmotic  currents  will  set  in.  Water  will  tend  to 
flow  into  the  egg  and  bits  of  salt  and  albumin  out  into  the 
water.  But  as  albumin  is  practically  non-dialyzable,  much 
more  water  will  flow  in  than  albumin  out,  and  so  the  contents 
of  the  egg  will  increase  in  size  and  the  partially  collapsed 
shell  membrane  again  be  distended  as  it  was  in  the  fresh  egg. 
If  these  osmotic  currents  are  allowed  to  continue,  the  result 
will  soon  be  that  the  shell  membrane  will  be  burst  by  the 
increased  pressure  caused  by  the  water  which  the  osmotic 
currents  have  carried  into  it. 

When  it  was  just  stated  that  absorption  in  the  alimentary 
canal  has  the  vitality  of  the  epithelium  cells  as  an  import- 
ant factor,  it  was  not  intended  to  deny  the  prominent  role 
played  by  osmotic  currents.  Thus,  a  draught  of  water 
readily  passes  into  the  blood,  110  doubt  for  the  reason  that 
23 


354  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  blood  is  saltier  than  the  pure  water,  and  so  the  water 
in  osmotic  currents  flows  into  the  blood.  On  the  other 
hand,  if  sufficient  salty  water  should  have  been  drunk  and 
the  contents  of  the  alimentary  canal  become  saltier  than  the 
blood,  water  would  run  from  the  blood  into  the  alimentary 
canal  and  the  thirst  be  exaggerated.  These  osmotic  cur- 
rents explain  the  physiological  action  of  certain  salts  which 
are  sometimes  prescribed  by  the  physician.  Such  mineral 
salts,  usually  Epsom  salts,  increase  the  saltiness  in  the  in- 
testine so  greatly  that  currents  of  water  from  the  blood  pass 
into  the  intestine  and  thus  produce  the  medicinal  effects  of 
that  drug.  On  the  other  hand,  if  these  salts  were  injected 
into  the  blood  and  the  saltiness  of  the  blood  thereby  materi- 
ally increased,  larger  quantities  of  water  than  usual  would 
be  absorbed  from  the  intestine  and  so  constipation  produced 
or  exaggerated. 

To  trace  out  in  detail  these  processes  of  absorption,  it 
may  be  desirable  to  treat  of  each  class  of  foods  separately. 
It  is  not  necessary  to  call  attention  to  the  absorptive  pro- 
cess in  the  various  portions  of  the  alimentary  canal,  because 
experiments  conclusively  show  that  practically  all  the  ab- 
sorption occurs  in  the  small  intestine.  It  seems  a  little  re- 
markable at  first  to  find  that  practically  no  absorption  at  all 
occurs  in  the  stomach.  Experiments  have  been  made  over 
and  over  again  to  show  that  dialyzable  substances,  even 
water  itself,  are  absorbed  in  very  small  quantities  indeed 
from  the  stomach.  As  a  digestive  agent  it  has  an  import- 
ant role,  but  as  an  absorbing  organ  it  figures  little  indeed. 
Experiments  have  been  tried  on  animals  by  injecting  water 
into  the  stomach  and  keeping  it  there  an  hour  or  more,  and 
then  determining  how  much  of  it  had  been  absorbed  in  the 
meantime.  Such  experiments  show  that  but  a  trifling 
amount  is  thus  absorbed.  We  have  to  imagine,  therefore, 
that  nearly  all  of  the  liquids  and  dialyzable  substances 
which  we  take  into  the  stomach  and  which  seem  to  reach 
the  blood  so  quickly  are  at  once  passed  by  the  stomach  into 
the  duodenum  and  absorbed  from  that  place.  Even  alcohol 


ABSORPTION    AND   THK    ROUTES    OF   FOOD.  355 

is  not  readily  absorbed.  Traces  of  peptones  and  sugars, 
and  possibly  salts  may  be  absorbed  when  one  speaks  mathe- 
matically, but  for  practical  physiological  purposes  we  have 
to  turn  to  the  small  intestine  for  this  function. 

THE  ABSORPTION  OF  THE  PEPTONES. 

It  will  be  remembered  that  the  various  proteids  taken  in 
the  body  are  by  the  digestive  changes  of  the  pepsin  and 
trypsin  finally  converted  into  peptones,  leaving  out  of  con- 
sideration for  the  present  small  bits  of  peptones  which  have 
been  disintegrated  still  further  into  leucin  and  tyrosin. 
These  peptones  are  dialyzable,  and  so  there  seems  at  first 
no  difficulty  in  understanding  how  they  might  enter  the 
blood.  But  the  difficulty  presents  itself  quite  seriously  when 
it  is  recalled  that  peptones  are  not  found  in  the  blood  any- 
where, not  even  in  the  blood  coming  directly  from  the  in- 
testines. Evidently  these  peptones  are  changed  after  leaving 
the  intestine  and  before  reaching  the  blood.  In  fact  pep- 
tones injected  into  the  blood  are  poisonous.  The  blood 
coming  from  the  intestines  and  carrying  the  absorbed  food 
contains  not  a  trace  of  peptone,  but  contains  those  albumens 
of  the  blood  treated  at  length  in  the  chapter  on  coagu- 
lation. It  is,  therefore,  evident  that  the  peptones  were 
changed  back  into  albumens  in  the  act  of  passing  through 
the  intestinal  walls.  Experiments  have  been  made  to  dem- 
onstrate this  fact.  Portions  of  fresh  intestine  have  been 
removed  from  the  body,  filled  with  a  solution  of  peptones, 
and  the  ends  tied.  This  intestine  was  then  immersed  in  a 
liquid  containing  not  a  trace  of  peptones  and  allowed  to 
remain  there  until  most  of  the  peptones  had  disappeared  in 
the  intestine,  but  not  a  trace  of  peptone  was  found  in  the 
outside  solution.  Here  it  was  present  in  the  form  of  albu- 
mens. It  would  be  interesting  to  know  in  what  manner  this 
change  was  effected.  Is  it  due  to  the  action  of  the  epi- 
thelium cells?  Is  it  a  change  brought  about  by  the  lym- 
phatic tissue  which  is  so  plentiful  in  the  walls  of  the 
intestine?  These  questions  are,  however,  much  more  easily 


356  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

asked  than  answered.  The  physiological  significance  of 
this  change  from  peptones  into  the  albumens  of  the  blood 
is  apparent.  In  the  first  place  the  peptones  act  as  poisons 
in  the  blood.  In  the  second  place,  being  changed  back  into 
albumens  they  are  robbed  of  their  dialyzing  power,  and  so 
there  is  prevented,  possibly,  the  loss  of  the  albumens  in 
kidneys  or  glands,  or  even  back  again  into  the  intestine,  for 
peptones  would  dialyze  into  the  intestine  as  easily  as  out 
of  it. 

THE  ABSORPTION  OF  THE  SUGARS. 

No  serious  difficulty  presents  itself  in  understanding  the 
absorption  of  the  sugars.  By  the  digestive  actions  of  the 
ptyalin  and  the  amylopsin,  all  the  starches  are  changed 
to  maltose,  and  finally  by  the  action  of  the  ferment  in  the 
intestinal  juice  all  the  various  sugars  taken  in  our  diet,  and 
the  maltose  derived  from  the  starch  are  changed  into  dex- 
trose or  grape  sugar  in  their  passage  through  the  abdominal 
wall.  In  the  form  of  dextrose  it  reaches  the  blood,  and  by 
the  portal  circulation  is  carried  to  the  liver,  where  it  is 
affected  in  a  manner  soon  to  be  described. 

THE  ABSORPTION  OF  THE  FATS. 

A  greater  difficulty  presents  itself  in  understanding  the 
absorption  of  fats.  That  portion  of  the  fats  which  is 
saponified  and  so  rendered  soluble  (for  soaps  are  soluble), 
will  readily  dialyze  into  the  blood,  but  most  of  the  fat  is  ab- 
sorbed in  its  solid  form;  that  is,  in  the  form  of  finely 
emulsified  droplets.  A  histological  examination  of  the 
small  intestine  during  fat-absorption  shows  droplets  of  fat 
in  the  epithelium  cells,  between  them,  and  even  under  them, 
reaching  into  the  lacteals.  It  is,  of  course,  out  of  the  ques- 
tion here  to  speak  of  physical  osmosis.  Droplets  cannot 
filtrate.  We  are  driven  to  the  conclusion  that  it  is  the 
epithelium  cells  that  line  the  intestine  which  actively  pick 
them  up;  that  is,  ingest  these  droplets  of  fat  into  their 
bodies,  pass  them  along  through  their  protoplasm,  and 
finally  eject  them  again  from  the  under  side  into  the  spaces 


ABSORPTION    AND    THK    ROUTES    OF   FOOD. 


357 


leading  to  the  central  lacteal.  The  droplets  of  fat  are 
pushed  in  some  inexplicable  way  through  the  epithelium 
cells  towards  the  central  lacteal.  Possibly  the  epithelium 
cells  pick  up  these  droplets  of  fat  much  as  the  amoeba  picks 
up  its  food. 

Additional  factors  in  fat  absorption  are  the  white  cor- 
puscles, so  plentifully  distributed  in  the  wall  of  the  intes- 
tine. It  is  believed  (and  there  is  fairly  good  histological 
evidence  for  this  belief)  that  the  corpuscles  wander  in  be- 
tween the  epithelium  cells,  ingest  particles  of  fat  like  an 
amoeba,  and  then  wander  back  through  the  interstices  of 
the  tissue  and  drop  their  load  of  fat  into  the  central  lacteal, 
accomplishing  this  by  disintegrating  themselves  and  so  lib- 


Fig.  126.— SECTION-  OF  A  FROG'S  INTESTINE  TREATED  WITH  OSMIC  ACID  TO  SHOW  AB- 
SORPTION OF  FAT.     (After  Schafer.) 
I,  lacteal;  c,  white  corpuscles  with  contained  fat  granules;  ep,  intestinal  epithelium; 

Kt>\  its  striated  border.     The  fat  granules  become  smaller  and  smaller  as  they  approach 

the  lacteal. 

crating  their  contained  fat.  On  sections  of  the  villi  one 
may  frequently  see  these  white  corpuscles  with  contained 
fat  droplets  in  all  positions  ranging  from  between  the  epi- 
thelium cells  to  the  central  lacteal. 

But  all  the  fat  suffers  a  peculiar  change  in  its  passage 
into  the  lacteal.  In  the  intestine  it  was  in  the  form  of  drop- 
lets. In  the  lacteal  it  is  in  the  form  of  small  particles  as 
fine  as  the  finest  dust.  But  not  only  this  mechanical  change 
has  occurred;  there  has  been  a  chemical  one.  In  the  lac- 
teal the  fat  is  not  present  as  butter,  or  lard,  or  tallow, 
forms  in  which  it  was  taken  in  the  food,  but  has  been 


358  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

changed  into  that  peculiar  form  of  fat  characteristic  of  the 
animal  which  has  eaten  it.  In  the  human  body  these  dust 
particles  of  fat  in  the  lacteal  are  now  no  longer  butter  and 
lard,  but  are  human  fat.  As  with  so  many  other  things  we 
still  have  no  knowledge  of  the  manner  in  which  this  chemi- 
cal change  is  effected.  It  may  be  in  place  to  call  attention 
to  the  fact  that  but  little  fat  reaches  the  blood  vessels. 
Practically  all  of  it  is  carried  by  the  lacteal.  These  vessels 
owe  their  name  to  the  circumstance  that  after  a  meal  they 
are  usually  filled  with  a  white  milky  substance,  the  particles 
of  fat  in  question.  It  was  formerly  believed  that  they  ab- 
sorbed all  the  food,  and  so  were  erroneously  called  absorb- 
ents. We  know  that  the  proteids,  and  the  sugars,  and  the 
albumens  are  carried  by  the  portal  circulation  to  the  liver. 

It  has  been  pointed  out  by  some  physiologists  that  pos- 
sibly the  involuntary  muscular  tissue  found  in  the  villi  of 
the  intestine  produces  a  kind  of  contraction  and  expansion 
of  each  villus,  and  so  the  central  lacteal  is  enabled  to  suck 
or  force  the  fat  into  itself.  These  contractions  of  the  villi, 
they  hold,  may  be  due  to  the  stimulation  caused  by  the  bile, 
and  in  this  way  they  explain  the  observed  fact  that  bile 
seems  to  aid  in  the  absorption  of  fats.  Through  these  lac- 
teals  the  fat  is  carried  towards  ,the  thoracic  duct,  and  by 
this  poured  into  the  left  subclavian  vein  and  so  distributed 
by  the  circulation.  The  further  changes  which  this  fat 
undergoes  will  be  discussed  later. 

The  various  salts,  the  water  and  the  albuminoids  in  the 
form  of  gelatin,  present  no  difficulties  in  their  absorption 
and  need  not  be  further  treated. 

When  finally  all  foods  have  been  absorbed  the  following 
is  the  state  of  things : 

First.  The  peptones  changed  back  into  the  albumens 
are  carried  by  the  portal  circulation  to  the  liver. 

Second.  All  the  sugars  changed  into  dextrose,  are  also 
carried  by  the  portal  circulation  to  the  liver. 

Third.  The  various  salts  and  the  water  drop  into  the 
portal  circulation  largely;  possibly,  also,  the  soluble  soaps, 
the  glycerine  and  the  albuminoids. 


ABSORPTION    AND    THE    ROUTES    OF   FOOD.  359 

Fourth.  The  emulsified  fats  changed  physically  and 
chemically  are  carried  by  the  lacteal  and  thoracic  duct  and 
dropped  into  the  general  circulation. 

We  have  now  to  consider  the  physiological  consequence 
of  the  transfer  of  these  sugars  and  proteids  to  the  liver  be- 
fore reaching  the  circulation  at  large. 

THE  GENERAL  PHYSIOLOGY  OF  THE  LIVEE. 

Some  of  the  most  important  functions  of  the  liver  are  in 
connection  with  the  phenomena  of  general  assimilation,  and 
a  discussion  of  the  liver  from  this  standpoint  is  reserved  for 
the  next  chapter.  We  have  to  do  in  this  connection  only 
with  the  function  of  the  liver  as  it  affects  the  proteids  and 
the  carbohydrates  in  their  passage  through  it  into  the  body. 

1. — Glycogenic  Function.  The  most  apparent  function 
of  the  liver,  and  one  of  the  most  important  as  well,  is  its 
formation  of  glycogen.  Glycogen  resembles  very  much 
ordinary  starch  in  many  particulars,  and  is,  in  fact,  fre- 
quently called  animal  starch.  The  liver  forms  this  gly- 
cogen by  changing  the  dextrose  carried  to  it  by  the  portal 
vein,  into  this  compound.  The  point  to  the  formation  of 
this  glycogen  is  the  ability  of  the  liver  to  store  this  sub- 
stance in  its  cells  and  then  to  dole  it  out  to  the  blood  from 
time  to  time  as  it  is  needed.  It  would,  of  course,  be  prac- 
tically impossible  to  store  in  an  organ  flushed  with  circula- 
ting blood  dialyzable  dextrose,  but  by  changing  the  dextrose 
into  an  insoluble  starch  like  glycogen  it  is  easily  retained. 

The  question  might  naturally  arise  concerning  the  ne- 
cessity of  storing  any  of  the  dextrose  at  all,  and  the  objec- 
tions to  having  all  of  it  pass  into  the  general  circulation  at 
once.  These  questions  are  readily  answered.  In  the  first 
place,  quite  a  large  amount  of  each  meal  is  carbohydrate 
food,  and  if  all  this  in  the  form  of  dextrose  should  be  in- 
jected into  the  blood  at  once  it  would  materially  alter  the 
composition  of  the  blood  and  so  lead  to  nutritive  disturb- 
ances. The  prime  necessity  of  the  blood  is  a  practically 
uniform  composition.  In  the  second  place,  such  largely 


360  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

increased  amounts  of  sugar  in  the  blood  would  lead  to  dia- 
betic results  in  the  kidneys,  for  it  is  a  commonly  observed 
fact  among  physicians  that  an  excess  of  sugars  soon  reveals 
itself  by  a  sugary  elimination  from  the  kidneys.  To  avoid 
both  of  these  dangers  all  the  excess  of  sugar  immediately 
after  a  meal  is  stored  in  the  liver,  and  observations  have 
been  made  on  the  human  liver  showing  that  the  amount  of 
glycogen  so  stored  may  reach  10  per  cent,  of  the  weight  of 
that  organ.  Then  during  the  interval  between  this  meal  and 
the  following  the  liver  doles  out  from  time  to  time  this  glyco- 
gen, and  so  serves  to  maintain  the  uniform  composition  of 
the  blood,  adding  the  glycogen  to  it  as  fast  as  the  sugar  is 
used  by  its  tissues.  This  addition  to  the  blood  is,  however, 
not  made  in  the  glycogen  itself,  but  this  is  converted  back 
into  dextrose  in  the  liver,  and  in  that  form  sent  into  the 
blood. 

This  glycogen  may  be  readily  detected.  It  may  be  seen 
microscopically  in  the  liver  cells  in  the  form  of  clear  lumps, 
which  when  treated  with  iodine  give  the  chemical  test  for 
glycogen.  Every  chemical  student  is  familiar  with  the 
fact  that  the  usual  reaction  to  detect  the  presence  of  starch 
is  to  treat  the  same  with  a  solution  of  iodine.  The  starch 
will  at  once  turn  a  very  deep  blue.  Glycogen,  however, 
does  not  turn  a  deep  blue,  but  turns  a  wine  red  color,  and 
in  this  way  is  easily  detected.  Unlike  starch,  too,  it  is 
somewhat  soluble  in  water;  more  readily  soluble  in  hot 
water,  and  by  this  means  the  glycogen  may  be  readily  ex- 
tracted from  minced  liver. 

It  will  be  seen,  therefore,  that  the  liver  is  a  kind  of 
store-house,  keeping  a  temporary  reserve  supply  of  glycogen 
to  be  used  up  in  the  intervals  between  meals.  It  is,  to  use 
a  common  figure,  the  pocket  change  to  supply  the  daily 
needs  of  the  tissue.  It  is  quite  interesting  to  note  that  the 
liver  is  not  the  only  organ  in  the  body  which  is  thus  able  to 
take  sugar  out  of  the  blood  and  store  it  up  within  itself  as 
a  reserve  supply  in  the  form  of  glycogen.  Glycogen  is 
found  in  other  parts  of  the  body.  In  white  corpuscles,  in 


ABSORPTION    AND    THE    ROUTES    OF    FOOD.  361 

the  placenta,  but  especially  in  the  voluntary  muscles. 
These  voluntary  muscles  seem  to  be  able  to  take  some  of 
the  sugar  out  of  the  blood  and  store  it  up  as  glycogen 
within  themselves  as  a  reserve  supply  to  fall  back  upon  in 
times  of  activity.  A  muscle  which  has  been  working  for 
some  time  loses  all  its  glycogen.  This  reserve  supply  has 
been  used  by  the  muscle  to  build  up  its  tissues.  It  is  an 
attempt  of  these  organs  to  have  at  their  immediate  disposal 
a  certain  reserve  supply  without  being  directly  dependent 
upon  the  blood-stream  at  critial  moments.  The  difference 
between  the  voluntary  muscles  and  the  liver,  however,  is 
that  the  reserve  supply  of  glycogen  in  the  muscles  is  in- 
tended merely  for  the  use  of  the  muscles,  while  the  liver 
acts  as  a  temporary  storehouse  for  the  entire  system. 

We  have  now  followed  the  sugar  into  the  liver,  watched 
its  change  into  the  animal  starch  called  glycogen,  saw  it 
stored  in  the  liver  cells  and  between  meals  doled  out  again 
to  the  blood  as  sugar.  What  further  change  this  sugar  suf- 
fers in  the  circulation  and  in  the  tissues  to  which  it  has  been 
carried  will  be  discussed  in  the  chapter  on  nutrition. 

2. — The  Albumens.  The  albumens,  too,  are  carried  to 
the  liver.  One  might  be  tempted  at  first  to  suppose  that 
the  sudden  excess  of  albumens  also  is  stored  here,  and  then 
like  the  sugar  is  dropped  back  into  the  blood  as  necessity 
requires.  But  there  is  no  place  in  the  body  where  albu- 
mens can  be  stored.  All  the  albumens  available  are  in  the 
circulating  blood  and  lymph.  Fats  may  be  stored  in  fatty 
tissue  and  remain  stored  there  for  a  long  time.  Sugars 
may  be  temporarily  stored  in  the  liver,  but  there  is  no 
storehouse  for  the  albumens.  These  must  drop  into  the 
general  circulation  at  once.  Here,  however,  the  danger 
would  present  itself  of  increasing  excessively  the  amount  of 
albumens  in  the  blood  after  a  meal,  and  so  producing 
nutritive  disturbances  here  as  well  as  with  the  sugars. 
Even  a  greater  danger  might  ensue.  The  accumulating 
albumens  of  the  blood  might  begin  to  be  eliminated  from 


362  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

the  kidneys  and  so  induce  B  right's  Disease  in  some  of  its 
forms.  The  point,  therefore,  is  to  regulate  in  some  way 
the  amount  of  albumens  in  the  blood  to  avoid  this  excess. 

As  the  albumens  cannot  be  stored  but  one  alternative  is 
left.  They  must  be  destroyed  as  albumens.  This  de- 
struction takes  place  in  the  liver.  Here  the  excess  of  the 
albumens  is  broken  up;  that  is,  disintegrated  chemically 
into  two  main  products.  One  product  contains  the  nitro- 
gen of  the  albumen  and  is  the  urea,  which  is  then  sent  to 
the  kidneys  to  be  eliminated.  The  other  part  is  a  non- 
nitrogenous  part,  and  is  by  the  liver  changed  into  fat  or 
sugar,  or  both,  and  so  made  possible  to  be  retained  in  the 
body.  Whether  this  non-nitrogenous  portion  of  the  excess 
albumen  is  changed  to  sugar  or  to  fat  seems  to  depend  to 
some  extent  upon  the  disposition  of  the  animal  in  this 
matter.  In  breeding  animals  for  fattening  purposes  special 
attention  is  paid  to  this  fact,  and  those  animals  are  selected 
which,  as  we  say  "fatten  easily, "  and  so  a  race  finally 
comes  to  be,  every  member  of  which  shows  a  tendency  to 
convert  all  extra  albumens  into  fat.  In  many  instances, 
however,  there  is  a  tendency  towards  the  formation  of 
sugar,  and  so  in  spite  of  the  richest  diet  but  little  headway 
is  made  in  laying  up  fat.  If  this  excess  is  turned  into 
sugar  in  the  liver  it  may,  of  course,  at  once  be  changed 
into  glycogen  and  so  stored  for  future  purposes.  If  it  is 
changed  into  fat  it  is  dropped  into  the  general  circulation 
and  distributed  over  the  body. 

We  have  thus  far,  then,  found  two  sources  of  the  gly- 
cogen in  the  liver.  The  first  and  main  source,  the  sugars 
of  the  body;  second,  a  derivative  from  the  excess  proteids. 
It  does  not  seem  possible  that  the  fats  are  able  in  any  way 
to  be  changed  into  the  glycogen.  This  change  of  the  pro- 
teids by  their  disintegration  ^or  burning  in  the  liver  into 
urea  and  into  glycogen,  has  a  medical  value  in  the  fact 
that  persons  suffering  with  diabetes  must  not  only  avoid  the 
carbohydrates,  but  must  be  equally  careful  not  to  take  an 
excess  of  ordinary  proteids  lest  the  formation  and  loss  of 


ABSORPTION   AND   THE    ROUTES   OF   FOOD.  363 

the  sugar  continue.  That  portion  of  the  proteids  taken 
which  is  needed  to  maintain  the  proper  composition  of  the 
blood  is  then  without  change  of  any  kind  allowed  to  pass 
through  the  liver  and  added  to  the  general  blood  stream. 

The  thing  in  the  albumens  which  makes  them  impos- 
sible to  be  stored  is  the  nitrogen  they  contain.  This  nitro- 
gen, as  pointed  out,  is  burned  into  the  substance  called 
"urea,"  is  then  allowed  to  drop  back  into  the  blood  stream, 
and  from  this  blood  stream  it  is  eliminated  by  the  kidneys. 
The  liver  is  therefore  the  seat  of  the  urea  formation.  But 
it  may  be  well  at  this  place  to  point  out  that  there  is  a 
second  source  from  which  the  liver  makes  its  urea.  This 
second  source  is  from  the  burned  up  tissues.  Various  pro- 
ducts of  tissue  disintegration  (and  tissues  are  largely  al- 
buminous) reach  the  liver,  and  by  the  liver  are  burned  into 
urea  and  then  sent  to  the  kidneys,  as  in  the  first  case.  The 
source  of  the  urea  is  therefore  a  double  one ;  one  directly 
from  the  burning  of  the  excessive  albumens  in  the  liver, 
the  second  from  the  burning  of  tissue  wastes  sent  to  the 
liver  from  all  the  organs  of  the  body.  The  liver  is,  there- 
fore, not  only  a  storehouse,  it  is  to  some  extent  also  a  cre- 
matory for  the  nitrogenous  wastes. 

The  final  state  of  things  is  then  as  follows : 
First.     Definite    amounts    of   the    albumens    have  been 
allowed  to    pass    through    the   liver   and    circulate   in    the 
blood. 

Second.  Quantities  of  dextrose  or  grape  sugar  are  from 
time  to  time  doled  out  from  the  reserve  supply  of  glycogen 
in  the  liver  and  dropped  into  the  blood  stream. 

Third.  Into  this  blood  stream  are  carried  all  the  fats 
absorbed  by  the  lacteals. 

Fourth.  In  this  blood,  too,  are  the  various  mineral 
salts  and  the  water  taken  in  the  foods. 

The  question  which  now  presents  itself  is,  in  what 
manner  are  these  nutritive  factors  of  the  blood  used  by  the 


364  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

tissues  ?  How  are  the  tissues  able  to  grow  by  taking  these 
substances  ?  How  are  they  able  to  derive  energy  and 
warmth  from  these  sources?  We  are  therefore  ready  to 
follow  somewhat  in  detail  the  phenomena  of  assimilation  in 
the  tissues  themselves. 


CHAPTER  XVI. 

NUTRITION  AND  THE  METABOLIC  CHANGES 
IN  THE  TISSUES. 

The  scene  of  activity  is  now  shifted  from  the  alimentary 
system,  from  the  liver,  and  even  from  the  circulating  blood 
and  directed  to  the  individual  living  cells  wherever  in  the 
body  they  may  occur.  Here  the  most  vital  part  in  the  his- 
tory of  the  foods  is  played;  it  is  here  where  the  food  is 
built  into  new  tissues ;  it  is  here  where  the  energies  of  the 
body  are  liberated. 

A  number  of  perplexing  questions  at  once  present  them- 
selves, the  solution  of  which  in  every  case  is  not  yet  forth- 
coming. Are  all  of  the  foods  taken  into  the  body  built  up 
into  living  tissue,  or  are  some  of  them  merely  oxidized 
without  ever  becoming  an  integral  part  of  the  body  ?  Is 
the  energy  derived  by  a  direct  oxidation  of  these  foods,  or 
is  the  energy  a  result  of  the  disintegration  of  living  ma- 
terial ?  When  oxygen  and  its  properties  were  first  dis- 
covered by  Priestly  and  Lavoisier,  the  conclusion  seemed 
irresistible  that  the  oxidations  of  the  body  occurred  in  the 
lungs.  According  to  this  view  it  was  explained  that  the 
animal  heat  originated  here,  and  was  by  the  circulating 
blood  carried  over  the  body,  and  in  this  manner  the  neces- 
sary energy  for  bodily  work  distributed.  It  was,  however, 
soon  found  that  the  blood  coming  from  the  lungs  was  not 
warmer  than  that  going  to  the  lungs,  and  so  this  view  had 
to  be  abandoned.  The  seat  of  oxidation  was  later  placed 
in  the  blood,  then  in  the  liver,  then  in  other  organs;  but 
there  is  no  question  at  all  now  but  that  the  seat  of  oxidation 
is  in  the  individual  living  cells  in  the  various  tissues  all 
over  the  body.  It  is  in  the  living  tissues  where  the  union 
of  the  foods  and  the  oxygen  occurs. 

(365) 


366  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

One  of  the  most  vital  questions  is  whether  these  living 
cells  can  take  some  of  the  food  out  of  the  blood  or  lymph, 
and  with  the  oxygen  from  the  lungs  produce  an  oxidation 
and  so  derive  heat  and  energy  for  their  own  use.  In  other 
words,  do  these  cells  manipulate  the  foods  like  the  fireman 
manipulates  his  coal?  If  so,  how  is  the  heat  of  such  an 
oxidation  transformed  into  the  kind  of  energy  needed,  be 
it  motion  or  be  it  chemical  changes  in  secretion  ?  Or  may 
not  the  foods  from  the  blood  and  the  oxygen  from  the  lungs 
be  built  up  in  the  living  cells  into  living  tissues,  and  then 
by  the  burning  up  or  chemical  disintegration  of  this  living 
matter  the  energy,  liberated  ?  To  use  a  not  very  close 
analogy,  are  the  foods  in  the  body  burned  like  the  coal  in 
the  furnace  to  heat  the  rest  of  the  house,  or  are  the  foods 
like  weather-boards,  shingles,  rafters  and  floors  built  into 
the  structure  of  the  house,  and  then  by  partial  oxidation 
heat  the  house  ?  Does  the  body  maintain  its  equilibrium 
of  temperature  and  derive  its  supply  of  energy  out  of  its  liv- 
ing supply,  or  from  the  external  foods? 

Of  course  there  is  no  question  at  all  as  to  what  happens 
to  some  of  the  foods  when  the  body  is  growing.  Evidently 
they  are  built  up  into  new  tissues.  The  increase  in  weight 
and  size  from  infancy  to  maturity  is  such  a  magical  trans- 
lation of  dead  food  matter  into  living  tissue.  The  question 
is  here  merely,  are  all  the  foods  treated  in  this  way,  or  may 
a  part  be  used  merely  for  fuel  purposes.  Unfortunately 
physiologists  seem  unable  to  agree  on  this  point.  There 
are  not  lacking  some  who  maintain,  and  apparently  with 
good  evidence,  that  a  large  part  of  the  food  is  directly  oxi- 
dized in  the  tissues  under  the  influence  of  the  living  cell 
without  that  food  ever  becoming  an  integral  part  of  those 
cells.  They  maintain  that  a  proportion  of  the  food  circula- 
ting in  the  blood  circulates  as  fuel,  while  another  part,  not 
different  in  kind,  however,  is  destined  to  be  built  up  into 
tissue.  They  look  upon  the  problem  of  nutrition  as  an  in- 
stance of  the  carpenter  who  uses  part  of  his  lumber  to  con- 
struct his  building  and  a  second  part  of  the  lumber  to  burn 


NUTRITION  AND  THE  CHANGES  IN  THE  TISSUES.       367 

in  his  furnace  to  heat  the  building.  According  to  this  view 
the  proteids  or  albumens  of  the  blood  are  looked  upon  as 
the  source  of  the  new  tissues,  while  the  remaining  albu- 
mens not  so  needed,  and  the  fats  and  carbohydrates  are 
used  for  direct  oxidation  purposes  only. 

Acknowledging  that  we  are  not  yet  able  to  answer 
definitely  these  intricate  questions,  there  seems  a  good 
deal  of  probability  that  this  view  is  not  entirely  correct. 
Repeated  and  careful  experiments  seem  to  lead  to  the  con- 
clusion that  under  normal  circumstances  all  of  the  foods  are 
first  built  into  living  tissue  and  then  oxidized.  The  marked 
exception  to  this  is  in  the  case  of  excessive  proteids  taken 
into  the  body,  which  since  they  cannot  be  stored  and  must 
be  eliminated,  must  be  burned  in  the  liver  in  the  manner 
indicated  in  the  preceding  chapter.  Here,  of  course,  is  a 
clear  instance  of  a  food  directly  oxidized  by  the  living  cells 
of  the  liver  without  ever  becoming  an  integral  part  of  that 
tissue.  But  it  would  hardly  be  right  to  look  upon  this  ex- 
cess of  proteid  as  a  food.  Its  very  disintegration  argues 
that  it  was  not  intended  as  a  food  but  was  eliminated  as  an 
injurious  ingredient.  The  normal  amount  of  proteids,  how- 
ever, of  the  blood,  as  well  as  the  sugars  and  the  fats,  and 
of  course  the  oxygen,  must  all  be  looked  upon  as  tissue 
formers.  But  with  the  exception  of  certain  special  tissues  in 
the  body,  such  as  the  supporting  tissues,  all  are  essentially 
albuminous  in  their  nature,  and  it  seems  at  first  difficult  to 
understand  how  the  fats  and  the  sugars,  which  are  not  at 
all  albuminous,  containing  no  nitrogen  whatever,  could 
possibly  be  built  into  living  tissues  which  are  albuminous, 
that  is,  contain  nitrogen. 

In  the  case  of  the  proteids  this  difficulty  is  absent.  We 
must  imagine  a  peculiar  constructive  chemical  process 
going  on  in  the  living  cell  by  means  of  which  the  proteid 
from  the  lymph,  possibly  with  some  salts,  is  combined  with 
the  oxygen  and  built  up  into  some  highly  complex  sub- 
stance which  we  call  protoplasm.  Just  as  in  the  manu- 
facture of  gunpowder  the  charcoal  and  the  oxygen  contained 


368  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

in  the  nitre,  together  with  the  other  substances,  are  mixed 
together  in  such  a  way  as  to  hold  a  large  amount  of  latent 
energy.  Gunpowder  possesses  enough  oxygen  within  itself 
to  burn  itself  up  completely.  In  fact,  it  is  this  intra-molar 
oxidation  which  is  the  explosion.  Gunpowder  explodes  be- 
cause in  every  part  of  its  substance  there  is  enough  oxygen 
present  to  burn  up  the  other  ingredients. 

So  we  must  imagine  that  the  living  cell  is  able  in  some 
at  present  entirely  inexplicable  way  to  take  dead  proteid 
and  salts  and  to  combine  these  with  the  oxygen  from  the 
lung  in  such  a  way  that  a  kind  of  living  gunpowder  pos- 
sessing much  latent  energy  is  produced.  This  view  of  the 
use  of  the  oxygen  from  the  lung  changes  completely  the 
current  notion.  Usually  we  speak  of  the  necessity  of  get- 
ting more  oxygen  in  exercise  in  order  that  there  may  be  a 
larger  supply  of  this  gas  to  burn  up  the  tissues  and  so  pro- 
duce the  energy.  According  to  this  view  (and  there  is 
every  probability  that  it  is  the  correct  one)  the  extra  de- 
mand of  the  oxygen  in  exercise  results  from  the  necessity 
of  building  up  new  living  tissue,  of  making  new  living  gun- 
powder to  replace  that  which  has  been  used  up  in  the  exer- 
cise in  question.  The  oxygen,  then,  is  not  the  cause  of  the 
liberation  of  the  energy;  it  is  the  result.  Just  as  in  a  bat- 
tle there  would  be  greater  demands  for  fresh  supplies  of 
gunpowder  to  replace  the  increased  amounts  being  used  up. 

This  constructive  building  up  of  proteids  and  oxygen 
into  living  matter  does  not  present  the  difficulties  which  at 
once  appear  when  we  think  of  the  sugars  and  the  fats.  The 
question  arises,  in  what  manner  do  these  foods  figure?  In 
the  first  place  it  is  well  to  remember  that  according  to  this 
view  proteids  alone  can  build  up  new  tissue.  Sugars  and 
fats  by  themselves  cannot  do  so.  Of  course  such  a  thing  is 
a  chemical  absurdity.  We  must  therefore  credit  to  the  pro- 
teid every  bit  of  new  tissue  that  appears,  and  imagine  its 
appearance  in  the  manner  just  indicated. 

The  main  characteristic  of  living  tissue  is  its  ability 
to  do  some  kind  of  work.  Life  in  this  sense  is  energy, 


NUTRITION  AND  THK  CHANGES  IN  THE  TISSUES.       369 

either  stored  up  or  in  action.  When,  now,  these  tissues 
are  called  upon  for  work  of  any  kind  the  energy  to  accom- 
plish this  is  derived  from  the  chemical  disintegration  of  a 
part  of  its  living  tissue,  just  as  energy  might  be  derived 
by  the  chemical  disintegration  of  a  bit  of  nitro-glycerine. 
We  have  therefore  to  look  upon  all  manifestations  of  the 
energy  in  the  body,  be  it  muscle,  or  nerve,  or  gland,  as 
a  disintegration  and  burning  up  and  dying  of  a  part  of 
this  tissue.  In  such  a  chemical  disintegration  a  good  deal 
of  energy  is  liberated,  partly  in  heat  to  maintain  the  tem- 
perature of  the  tissues,  or  in  the  case  of  the  muscles,  in 
additional  energy  to  contract  them.  The  products  of  such 
a  chemical  disintegration  are  mainly  as  follows: 

The  carbon  of  the  living  tissue  appears  as  carbon  dioxide COz 

The  hydrogen  as  water HaO, 

And  the  nitrogen  in  the  form  of  a  compound  closely  related 
to  urea. 

The  carbon  dioxide  is  of  course  at  once  removed  through 
the  lungs  in  the  manner  explained  at  great  length  in  the 
chapter  on  respiration.  The  water  drops  into  the  blood  and 
is  so  lost  track  of,  but  the  urea-like  product,  this  remnant 
which  contains  the  nitrogen  of  the  living  molecule,  is  not 
lost  from  the  tissue,  but  is  retained.  The  living  cell  which 
retains  this  nitrogenous  remnant  of  the  disintegration  is 
able  to  use  this  remnant  again  to  build  up  'new  living  tis- 
sue. It  is  able  to  use  the  same  nitrogen  over  again  and 
needs  only  a  new  supply  of  carbon,  hydrogen  and  oxygen 
to  replace  the  amounts  of  these  substances  lost  in  the  car- 
bon dioxide  and  the  water.  This  supply  of  carbon,  hydro- 
gen and  oxygen  it  is  able  to  take  from  either  the  fats  or 
sugars  of  the  blood  and  the  oxygen  constantly  brought  from  the 
lungs.  The  living  cell  is  able  to  re-combine  the  nitrogenous 
remnant  with  the  carbon,  oxygen  and  hydrogen  derived 
from  the  sugars  or  fats,  and  an  added  amount  of  oxygen 
from  the  lungs  into  a  new  living  tissue  molecule  having  the 
same  composition  as  the  original.  This  molecule  may 
again  under  nervous  or  other  influences  be  dissociated  and 
24 


370  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

so  give  rise  to  the  liberation  of  new  energy,  carbon  dioxide 
and  water  being  the  result,  as  in  the  first  case,  but  the  ni- 
trogenous remnant  being  again  saved  and  by  combination 
with  new  fats  or  sugars  and  the  oxygen  from  the  lungs,  be 
built  for  a  second,  a  third,  or  fourth  time  into  living  tissue. 
If  this  view  is  correct  it  would  explain  why  the  loss  in  nitro- 
gen does  not  vary  with  the  work,  a  man  resting  eliminating 
from  his  body  about  as  much  as  a  man  working. 

When  it  is  said  that  the  nitrogenous  remnant  is  saved, 
there  is  to  be  added  that  a  small  portion  of  this  nitrogenous 
remnant,  however,  is  lost;  some  possibly  accidentally  car- 
ried away  by  the  circulating  fluid,  some  possibly  chemically 
unfit  to  be  used  again.  It  is  this  little  loss,  this  wear  and 
tear,  which  is  sent  to  the  liver  and  in  the  liver  is  burned 
into  urea  and  then  eliminated  from  the  kidney.  But  this 
wear  and  tear  may  almost  be  as  much  in  a  resting  person 
as  in  an  active  person,  just  as  the  wear  and  tear  of  an  en- 
gine that  is  in  proper  use  may  not  exceed  the  wear  and  tear 
of  an  engine  standing  idle  on  the  sidetrack. 

Some  interesting  experiments  have  been  made  showing 
that  the  loss  of  the  nitrogen  from  the  body  is  not  at  all 
proportional  to  the  work  done.  Persons  have  ascended 
mountains  and  during  the  period  of  such  exertions,  as  well 
as  before  and  after,  careful  quantitive  determinations  were* 
made  of  the  amount  of  urea  eliminated  from  the  kidneys. 
It  was  found  that  even  in  such  laborious  work  as  mountain 
climbing  the  nitrogenous  loss  from  the  body  was  not  pro- 
portionately larger,  in  fact  hardly  materially  larger  than  the 
loss  while  resting.  On  the  view  just  given  of  the  manner 
in  which  the  nitrogen  is  used  over  and  over  again  this  is 
readily  understood. 

The  amount  of  carbon  dioxide  produced,  and  of  course 
the  water,  is  however,  directly  proportional  to  the  amount 
of  work  done.  At  each  chemical  disintegration  a  certain 
amount  of  carbon,  oxygen  and  hydrogen  is  lost,  which  must 
be  replaced  in  the  next  constructive  process  by  an  equal 
amount  of  new  material.  Evidently,  therefore,  the  amount 


NUTRITION  AND  THE  CHANGES  IN  THE  TISSUES.       371 

of  this  carbon,  hydrogen  and  oxygen  will  be  proportional  to 
the  amount  of  work  done.  This  at  once  explains,  too, 
the  increased  breathing  of  oxygen  with  increased  exertion, 
and  also  explains  the  necessity  for  increased  amounts  of  food 
with  increased  exertion. 

But  such  an  increase  of  foods  need  not  at  all  be  proteid, 
but  may  be  fatty  or  carbohydrate.  Of  course  a  certain 
amount  of  proteid  is  absolutely  indispensable,  since  proteid 
alone  can  replace  the  slight  wear  and  tear  just  referred  to. 
To  eat  more  proteid  food  than  necessary  to  replace  this  loss 
simply  necessitates  the  body  to  eliminate  it.  In  physiolog- 
ical terms  we  speak  of  a  person  or  animal  as  being  in  a  pro- 
teid equilibrium  when  the  nitrogen  taken  in  his  foods  equals 
in  amount  the  nitrogen  eliminated  from  the  kidneys.  In 
the  same  way  we  speak  of  a  person  as  being  in  a  carbon 
equilibrium  when  the  carbon  taken  in  his  foods  is  equal  to 
the  carbon  eliminated  from  his  lungs.  If  more  is  eliminated 
than  is  taken  in  in  any  of  these  cases  starvation  and  emacia- 
tion are  the  result.  If  more  of  these  foods  is  taken  than  is 
needed  one  or  both  of  two  results  may  follow:  Some  of 
the  surplus  food,  as  for  instance  the  fat,  may  be  stored  in 
the  tissues  for  future  use  and  so  the  person  become  fat,  in 
the  ordinary  use  of  that  term;  or  secondly,  the  nutritive 
equilibrium  of  that  individual  raised  to  a  higher  level.  This 
needs  a  word  of  explanation.  It  is  possible  in  a  long  con- 
tinued diet  to  establish  a  nutritive  equilibrium  at  an  almost 
starvation  diet.  The  tissues  of  the  body  will  adjust  them- 
selves to  the  income,  and  finally  establish  an  equilibrium  at 
that  level.  This  means  that  the  losses  will  exactly  balance 
the  gains  and  the  body  will  seem  to  hold  its  own.  If,  now, 
the  amount  and  quality  of  the  foods  be  suddenly  increased, 
there  is  at  first  a  tendency  of  the  body  to  eliminate  these 
extra  foods,  especially  the  proteids,  but  finally  the  tissues 
will  adjust  themselves  to  the  new  order  of  things,  will  use 
up  increased  quantities  of  food  in  their  daily  work,  until 
finally  a  new  nutritive  equilibrium  is  established.  As  a  sim- 
ple analogy  an  illustration  may  be  taken  from  the  social 


372  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

world :  Persons  are  able  to  maintain  a  financial  equilibrium 
with  a  small  income,  but  there  is  no  difficulty  at  all  in  soon 
adjusting  one's  self  to  an  added  income  and  so  establishing 
an  equilibrium  on  a  higher  level. 

But  this  does  not  always  mean  that  when  a  body  is  not 
losing  in  weight  it  is  holding  its  own  in  the  fullest  sense. 
It  is  doing  so  at  a  low  nutritive  level,  but  it  is  still  starva- 
tion, and  the  general  beneficial  effects  that  are  recognizable 
in  a  community  of  well-fed  people  clearly  argues  the  physi- 
ological necessity  of  establishing  in  a  healthy  body  at  least  a 
medium,  still  better,  a  high  nutritive  equilibrium. 

These  metabolic  changes  and  the  final  products  have 
been  fairly  well  determined  only  in  the  case  of  muscular 
tissue.  What  the  final  chemical  changes  are  in  glands 
ganglia  and  in  nerve  fibers,  is  still  a  wholly  closed  book. 
However,  from  a  merely  physical  and  chemical  standpoint 
the  energies  liberated  by  the  muscles  are  by  far  the  bulk  of 
the  body's  whole  expenditure. 

By  way  of  summary,  then,  we  have  to  ascribe  to  the 
main  classes  of  foods  these  nutritive  values: 

First.  Proteids. — (a)  All  new  tissue,  that  is,  all  living  tis- 
sue which  has  not  replaced  the  old,  but  is  an  actual  addition, 
can  only  be  built  up  from  the  proteids  of  the  blood  and  lymph. 
Hence  the  somewhat  larger  proportion  of  proteids  needed 
in  the  diet  of  animals  which  are  in  the  growing  period. 
(b)  Excesses  of  proteids  are  broken  up  in  the  liver  into  a 
non-nitrogenous  portion  which  may  appear  there  as  sugar 
or  as  fat,  and  a  nitrogenous  portion  appearing  as  urea.  The 
sugar  or  fat  so  produced  from  these  proteids  will  then  figure 
just  as  the  other  fats  and  sugars. 

Second.  The  Albuminoids.  These  do  not  figure  in  an 
important  way,  and  it  is  highly  improbable  that  the  nitro- 
gen which  they  contain  can  in  any  material  way  be  utilized 
like  the  nitrogen  of  proteids.  Probably  the  albuminoids 
figure  in  the  same  role  as  the  sugars  and  the  fats. 

Third.     TJic  Sugars  and  the  Fats.     These  are  the  non- 

<D 

nitrogenous  foods,  but  in  the  tissues  these  non-nitrogenous 


NUTRITION  AND  THE  CHANGES  IN  THE  TISSUES.       373 

foods  are  combined  under  the  influences  of  the  living  cell 
with  the  nitrogenous  remnant  there  of  a  previous  disintegra- 
tion, and  so  built  up  into  living  tissue.  These  sugars  and 
fats  supply  that  part  of  the  food  which  in  the  disintegration 
of  the  living  tissue  is  lost ;  they  supply  the  carbon  and  the 
hydrogen.  As  these,  therefore,  cannot  be  used  a  second 
time,  new  amounts  of  sugars  or  fats  must  be  taken  to  replace 
them.  In  this  way  the  consumption  of  sugars  and  fats  of 
the  blood  must  be  proportional  to  the  amount  of  work  done. 
Of  course,  if  sugars  and  fats  are  not  given  in  sufficient 
amounts,  or  are  excluded  altogether,  the  body  is  able  to 
derive  this  oxygen,  carbon  and  hydrogen  from  proteids 
alone.  But  then  this  great  excess  of  proteid  must  be  first 
dissociated  in  the  liver,  and  so  sugar  or  fat  produced,  and 
these  be  the  immediate  foods  of  the  tissues.  Carnivorous 
animals  can  live  upon  a  diet  of  meat  alone,  and  in  such  cases 
the  quantity  of  meat  will,  to  a  large  extent,  be  proportional 
to  the  work  done.  But  the  proportion  is  not  in  the  nitrogen 
which  it  contains,  but  in  the  carbon  and  hydrogen  which 
are  needed. 

An  ideal  physiological  diet,  therefore,  is  one  that  con- 
tains enough  proteid  to  replace  the  wear  and  tear  of  the 
body  on  a  high  nutritive  equilibrium,  and  then  has  the  car- 
bohydrates and  fats  as  the  sources  from  which  the  carbon 
and  hydrogen  are  derived.  Increased  work,  therefore,  would 
demand  not  primarily  an  increase  in  the  proteids,  but  would 
at  once  demand  a  proportional  increase  in  the  fats  and 
sugars. 

It  was  pointed  out  that  a  little  of  the  nitrogenous  rem- 
nant which  results  from  the  disintegration  of  a  part  of  the 
living  cell  is  lost,  possibly  accidentally,  more  probably  be- 
cause it  is  no  longer  fit  to  be  used.  This  nitrogenous  rem- 
nant no  longer  retained  by  the  cell  is  dropped  into  the  blood 
and  is  by  the  blood  carried  to  the  liver.  This  substance 
appears  in  several  different  stages  of  oxidation  and  is  known 
to  the  chemist  as  kreatin  or  kreatinin.  This  kreatin  aris- 
ing in  the  tissues  of  the  body  and  carried  to  the  liver  by  the 


374  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

blood  is  ill  the  liver  burned  still  further  into  urea,  and  then 
sent  to  the  kidneys  to  be  eliminated. 

We  have  thus  seen  two  sources  of  urea  in  the  body,  one 
derived  from  the  immediate  burning  up  of  the  excess  pro- 
teids  in  the  liver,  the  other  derived  from  the  kreatin  and 
similar  compounds  of  the  tissue  destruction.  But  the  for- 
mation of  this  urea  occurs  in  both  cases  in  the  liver.  The 
kidneys  take  no  part  whatever  in  the  production  of  this  sub- 
stance, but  are  concerned  wholly  and  only  with  its  elimina- 
tion. When  the  diet  is  naturally  rich  in  the  proteids,  and 
when,  therefore,  increased  amounts  of  these  urea-like  sub- 
stances appear  in  the  blood,  the  kidneys  are  frequently  un- 
able to  eliminate  this  from  the  body  as  rapidly  as  it  is  being 
formed,  and  so  there  is  a  tendency  towards  the  accumula- 
tion of  uric  compounds  in  various  parts  of  the  body,  especi- 
ally at  the  joints,  producing  the  somewhat  aristocratic 
disease  called  the  "  gout."  These  uric  poisons  in  the  blood 
serve  to  irritate  the  tissues  and  so  produce  quite  abnormal 
conditions.  The  remedy  is,  of  course,  the  removal  of  these 
poisonous  salts  from  the  blood.  One  of  the  best  agents  in 
the  physician's  hand  is  some  form  of  salicylic  acid,  in  which 
these  salts  are  soluble,  and  which  when  taken  into  the  blood 
tends  to  dissolve  them  out  of  the  tissues.  Along  with  such 
tendencies  to  gout  the  increased  demands  made  on  the  kid- 
neys may  finally  result  in  the  impairment  of  their  energies, 
and  so  Bright 's  Disease  be  induced,  a  disease  alarmingly 
frequent  among  persons  addicted  to  a  luxurious  table. 

Whether  the  familiar  rheumatism  is  due  to  an  accumula- 
tion of  metabolic  products  in  the  blood  is  still  unsettled. 
Some  look  upon  it  as  a  disease  due  to  germs,  others  as  a 
cold  affecting  nerve  centers,  and  by  still  others,  and  possi- 
bly most,  as  a  result  of  the  accumulation  of  lactic  acid  in 
the  blood.  It  has  even  been  claimed  by  one  observer  that 
it  was  possible  to  produce  rheumatism  artificially  by  an  in- 
jection of  lactic  acid  into  the  system. 


NUTRITION  AND  THE  CHANGES  IN  THE  TISSUES.       375 
THE  INTER- RELATION  OF  THE  FATS  AND  CARBOHYDRATES. 

It  was  of  course  long  known  that  a  proteid  diet  might 
result  in  the  fattening  of  an  animal;  also  that  proteids 
might  give  rise  to  sugar.  It  has  been  an  important  but 
difficult  question  whether  the  carbohydrates  ever  give  rise 
to  fats;  whether  a  sugary  diet  leads  directly  to  the  produc- 
tion of  fatty  tissues.  Until  very  recently  it  was  almost  uni- 
versally held  that  the  carbohydrates  could  not  form  fats  in 
the  body,  and  that  the  fattening  resulting  from  adding  a 
carbohydrate  food  was  due  merely  to  the  saving  of  fats, 
these  being  substituted  for  them.  Just  as  on  the  dinner 
table  it  might  be  possible  to  produce  an  accumulation  of 
bread  by  having  plenty  of  pie.  Of  late,  however,  investi- 
gations have  been  made  which  seem  to  show  that  carbohy- 
drates in  the  body  may  be  changed  into  fats  and  so  stored. 
Attention  is  here  called  to  this  claim  since  it  is  possible 
that  future  observations  may  establish  its  correctness;  but 
the  point  remains  that  in  spite  of  these  claims  there  is  much 
evidence  that  fats  are  never  the  direct  result  of  the  sugars 
or  the  sugars  of  the  fats,  and  that  there  is  in,  no  way  a 
direct  causal  relation  between  them. 

No  attention  has  been  given  to  the  nutritive  importance 
of  the  water  and  the  salts.  It  has  not  been  deemed  neces- 
sary to  go  into  detail  here.  Water  is  the  general  solvent  of 
the  body  and  the  medium  in  which  the  cells  live,  and  as 
such  is  absolutely  indispensable.  The  salts,  -too,  are  neces- 
sary parts,  frequently  being  directly  used  in  the  formation 
of  tissues,  as  in  the  case  of  bones  and  red  corpuscles,  or 
directly  serving  an  intermediate  function  in  the  process  of 
osmosis  or  solution. 

The  attempt  has  been  made  in  the  chapter  to  try  to  pic- 
ture the  phenomena  which  take  place  in  the  individual  liv- 
ing cells  while  these  cells  are  in  growth  or  action.  We 
have  now  to  determine  somewhat  more  quantitatively  the  re- 
sults of  the  energy  so  derived,  the  purposes  of  this  energy, 
especially  that  of  the  temperature  of  the  body,  and  finally 
the  manner  in  which  this  temperature  is  maintained  at  a 
steady  and  fixed  level  under  normal  conditions. 


CHAPTER  XVII. 


THE  MAINTENANCE  OF  THE  ANIMAL  HEAT. 

As  long  as  the  body  is  alive  heat  is  being  produced  in 
it.  Even  a  muscle  that  may  be  showing  not  a  bit  of  con- 
traction is  nevertheless  developing  a  certain  amount  of  heat. 
Heat  is  a  constant  product  of  the  transformation  of  energy 
in  the  body.  The  most  noteworthy  fact  in  examining  this 
heat-production  is  its  steady  maintenance  under  normal 
conditions.  Thus  the  temperature  of  an  average  adult  is 
about  37llio°C.)  and  this  temperature  is  maintained  through 
summer,  through  winter,  and  through  all  of  the  vicissitudes 
of  every-day  life  with  almost  mathematical  exactness. 

Animals  which  have  such  a  constant  temperature  are 
spoken  of  as  homothermous ;  that  is,  as  the  etymology  of 
the  word  shows,  of  constant  temperature.  Animals  pos- 
sessing a  constant  temperature  have  one  which  is  usually 
above  the  temperature  of  their  surroundings.  They  are 
warm-blooded.  This  is  true  of  nearly  all  the  higher  ani- 
mals. As  we  descend  the  scale,  however,  this  condition 
changes,  and  we  find  the  temperature  of  the  lower  animals 
determined  almost  wholly  by  their  immediate  environment. 
Their  temperature  rises  or  sinks  with  the  temperature  of 
their  surroundings.  Such  animals  are  called  poikilother- 
mous\  that  is,  of  several  temperatures.  More  frequently 
such  animals  are  spoken  of  as  cold-blooded  animals,  but  it 
not  infrequently  happens  that  the  temperature  of  such  a 
cold-blooded  animal  may  even  be  higher  than  that  of  a 
warm-blooded  animal,  provided  the  medium  in  which  it 
lives  rises  above  that  temperature.  Examples  of  cold- 
blooded animals  are  the  fishes,  amphibians  and  reptiles. 
(376) 


THE    MAINTENANCE    OF   THE    ANIMAL   HEAT.  377 

VARIATIONS  IN  TEMPERATURE. 

The  temperature  of  warm-blooded  animals  is  not  abso- 
lutely constant  by  any  means.  Thus,  mammals  which  go 
into  a  winter  sleep,  hibernate,  as  we  say,  have  their  tem- 
perature sink  several  degrees,  in  this  way  approaching  some- 
what the  cold-blooded  animals.  The  advantage  of  being 
able  to  lie  in  this  protracted  sleep  at  a  somewhat  reduced 
bodily  temperature  is,  of  course,  very  evident  when  we  re- 
member the  saving  of  tissue  on  this  account.  Some  of  the 
mammals  show  a  transition  to  the  lower  classes  in  their 
temperature.  Thus,  the  temperature  of  the  monotremes,  a 
group  of  animals  to  which  the  Duck-bill  belongs,  is  nor- 
mally no  higher  than  30°  C. 

There  are  also  differences  in  the  temperatures  of  differ- 
ent classes  of  warm-blooded  animals.  Thus,  as  a  rule,  the 
temperature  of  larger  animals  is  less  than  that  of  smaller 
ones.  In  the  case  of  birds  the  highest  temperature  is 
reached,  running  up  as  high  as  from  40°  to  45°  C.  This 
in  the  human  body  would  be  a  fever-heat  and  would  in  all 
probability  prove  fatal.  This  relatively  much  higher  tem- 
perature in  birds  no  doubt  facilitates  muscular  contraction, 
and  may  be  easily  explained  by  relating  it  to  the  flight  of 
birds. 

But  differences  in  temperature  may  occur  in  the  same 
individual.  Thus,  there  are  differences  on  account  of  age. 
The  temperature  of  an  infant  is  usually  the  highest,  being 
about  379/io°  C.  From  this  it  sinks  to  about  37Vio°,  which 
is  the  temperature  of  active  adult  life.  As  age  advances 
the  temperature  sinks  still  further,  and  at  seventy  is  about 
368/io°.  However,  in  real  old  age  it  begins  to  rise  again 
and  frequently  reaches  374/io°,  almost  the  temperature  of  an 
infant.  Numerous  observations  seem  to  show,  too,  that 
the  temperature  in  females  is  slightly  lower  than  in  males. 

There  are  even  differences  in  temperature  in  the  differ- 
ent regions  of  the  same  body,  the  highest  temperature  be- 
ing reached  in  the  liver  and  the  internal  glands,  where  it 
is  not  infrequently  and  normally  from  38°  to  39°  C.  The 


378  STUDIES    IX    ADVAXCKD    PHYSIOLOGY. 

lowest  temperature  is  in  the  most  exposed  portions  of  the 
skin,  such  as  the  ear  flaps,  where  on  account  of  the  ex- 
cessive radiation  of  heat  it  may  sink  materially. 

So  far  the  variations  in  temperature  have  been  normal 
variations.  In  addition,  however,  to  these  there  occur  the 
variations  caused  by  external  agents,  either  by  the  immedi- 
ate surroundings  or  by  pathological  conditions  within  the 
system.  The  limits  of  temperature  which  may  be  so  pro- 
duced are  considerable.  One  of  the  lowest  temperatures 
recorded  is  246/io°C.,  the  temperature  of  a  drunken  man. 
The  upper  limits  have  been  reached  in  fevers,  when  the 
temperature  may  rise  from  375/io°  to  415/io°  C.  Expressed 
in  Fahrenheit  degrees,  the  variations  in  temperature  are 
from  76°,  in  the  case  of  the  drunkard,  to  106°,  in  the  case 
of  fevers.  Sometimes  just  before  death  temperatures  from 
110°  to  113°  have  been  recorded. 

CONDITIONS  AFFECTING  THE  TEMPERATURE. 

The  temperature  is  affected  in  a  number  of  ways.  The 
first  and  most  apparent  agency  is,  of  course,  the  external 
environment.  The  temperature  is  higher  on  an  average  in 
summer  than  in  winter.  It  is  increased  by  taking  hot 
things  into  the  stomach,  or  by  subjecting  the  whole  body 
to  a  hot  bath. 

Secondly,  the  most  usual  agency  affecting  the  tempera- 
ture is  the  oxidation  in  the  body.  When  this  oxidation  in- 
creases, as  in  the  case  of  muscular  work  or  exertions  of  any 
kind,  the  temperature  increases  along  with  it.  It  is  the 
commonest  experience  of  course  that  hard  work  makes  one 
warm . 

A  third  agency  affecting  the  temperature  is  the  blood- 
flow,  especially  through  the  skin.  When  the  blood-vessels 
in  the  skin  are  dilated  and  much  blood  traverses  it,  it  is 
there  exposed  to  the  radiating  influences  and  is  materially 
cooled.  On  the  other  hand,  when  the  blood-vessels  of  the 
skin  are  contracted  and  little  blood  passes  through  there, 
much  less  opportunity  is  given  for  the  heat  to  radiate  from 


THE  MAINTENANCE  OF  THE  ANIMAL  HEAT.     379 

the  skin.  This  is  one  of  the  most  efficient  means  the  body 
has  to  maintain  its  temperature  equilibrium. 

One  of  the  deceptive  results  of  alcoholic  drinks  is  the 
feeling  of  warmth  experienced.  This  is  due  to  the  fact  that 
under  the  action  of  the  alcohol  the  blood-vessels  of  the  skin 
have  been  dilated  and  the  warm  blood  from  the  visceral 
organs  traverses  it,  giving  to  the  skin  its  sense  of  warmth. 
As  a  matter  of  fact,  however,  this  exposes  the  warm  blood 
to  the  exterior,  and  the  result  is  a  material  loss  of  bodily 
temperature  in  spite  of  the  deceptive  feeling. 

Fourth,  the  temperature  may  be  materially  affected  by 
the  administration  of  drugs.  It  may  be  increased  by  such 
drugs  as  atropine,  strychnine,  caffeine,  and  others;  on  the 
other  hand,  materially  decreased  by  quinine,  morphine, 
large  doses  of  alcohol  and  others.  These  medicinal  prop- 
erties of  drugs  frequently  enable  the  physician  to  increase, 
or  more  usually  in  cases  of  fevers,  to  decrease  the  tempera- 
ture from  a  dangerously  high  point  to  the  normal. 

There  is  no  question  any  more  but  that  the  temperature 
of  the  body  may  be  directly  affected  by  nerves  carrying 
their  impulses  from  nerve  centers  especially  concerned  in 
the  regulation  of  the  bodily  heat.  These  thermogenic 
nerves,  as  they  are  called,  are  vital  agents  in  the  regulation 
of  the  temperature,  a  topic  which  naturally  arises  at  this 
point. 

THE  REGULATION  OF  THE  TEMPERATURE. 

Any  one  who  has  ever  had  any  practical  experience  in 
trying  to  maintain  a  uniform  temperature  in  a  room  or 
house,  even  with  the  best  modern  heating  appliances,  re- 
alizes the  great  difficulty  he  has  undertaken.  In  spite  of 
the  most  improved  modern  contrivances  and  in  spite  of 
constant  watching,  the  temperature  of  a  large  building  will 
vacillate  through  many  degrees  in  the  course  of  a  day. 
One  is  therefore  naturally  surprised  to  find  the  temperature 
of  the  body  subjected  in  so  many  different  ways  to  every 
change  in  external  conditions  remain  so  constant,  and  the 


380  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

question  naturally  arises,  in  what  manner  the  production  of 
this  heat  is  maintained  and  regulated  so  perfectly  ? 

The  agencies  which  figure  in  this  regulation  are  of  two 
kinds : 

1. — Artificial  Agencies.  Such  artificial  agencies  are, 
first,  clothing  and  fuel;  second,  increased  exercise.  It  is 
the  commonest  experience  to  maintain  the  temperature  of 
the  body  on  a  cold  day  by  increasing  vigorously  the  amount 
of  exercise.  Third,  with  the  approach  of  cold  weather  we 
change  more  or  less  consciously  the  kind  and  quantity  of 
foods,  eating  in  winter  as  a  rule  not  only  more  food,  but 
food  of  greater. heat-producing  quality.  Fourth,  as  pointed 
out  just  above,  we  may  regulate  the  temperature  to  some 
extent  by  the  administration  of  drugs,  a  regulation  fre- 
quently called  in  in  the  reduction  of  temperatures  in  feverish 
conditions. 

2. — Natural  Agencies.  The  second  group  of  agencies 
are  those  which  might  be  designated  as  the  natural  ones ; 
that  is,  agencies  which  come  into  play  without  our  con- 
scious intervention.  These  are,  first,  an  increased  activity  of 
the  heart  and  lungs  in  cold  weather;  second,  contraction 
or  relaxation  of  the  capillaries  of  the  skin;  third,  the  per- 
spiration of  the  skin,  in  the  evaporation  of  which  much  heat 
may  be  eliminated  from  the  body;  fourth,  a  natural  in- 
creased hunger;  fifth,  involuntary  movements,  such  as  the 
familiar  shivering  and  chattering  of  teeth  which  follow  un- 
clue  exposure  to  cold;  sixth,  the  thermogenic  nerves. 

THERMOGENIC  NERVES. 

It  has  now  been  settled  beyond  a  matter  of  question  that 
there  are  nerves  in  the  body  which  are  concerned  directly 
with  the  production  of  heat.  The  centers  from  which 
these  thermogenic  nerves  arise,  lie  probably  in  the  spinal 
cord.  These  centers  in  the  spinal  cord  may,  however,  be 
stimulated  or  inhibited  by  higher  centers  lying  in  the  brain 
and  medulla.  Repeated  experiments  in  this  direction  seem 


THE  MAINTENANCE  OF  THE  ANIMAL  HEAT.     381 

to  indicate  that  there  are  heat-accelerator-centers  as  well  as 
heat-inhibitory -centers.  These  have  been  localized  especi- 
ally in  the  region  of  the  floor  of  the  brain  occupied  by  the 
corpora  striata.  These  centers  in  a  reflex  way  stimulate 
the  centers  of  the  spinal  cord  to  greater  heat  production,  or 
inhibit  them  and  so  lessen  the  heat  production.  In  this 
way  it  is  believed  the  heat  equilibrium  is  so  successfully 
maintained. 

Under  normal  conditions  these  heat  centers  are  adjusted 
or  set  for  a  temperature  of  37l/io°  C.,  but  in  abnormal  con- 
ditions, such  as  fevers,  they  may  become  set  or  adjusted 
for  a  higher  temperature.  Experiments  on  the  lower 
animals  show  that  they  may  also  be  set  for  temperatures  be- 
neath the  normal.  It  would  be  interesting  to  know  just  what 
it  is  in  the  case  of  fevers  which  changes  the  readjustment 
of  these  centers  from  the  normal  point  to  the  fever  point. 
But  this  information  is  not  at  hand.  Possibly  some  of  the 
poisons  of  the  disease  may  act  as  an  irritant  upon  these 
centers  and  thus  disturb  the  equilibrium.  Unfortunately, 
too,  we  have  no  knowledge  yet  in  what  specific  manner 
such  drugs  as  quinine  act  in  the  reduction  of  these  fever 
temperatures. 

It  is,  of  course,  not  necessary  to  say  that  these  thermo- 
genic  nerves  running  to  the  various  tissues  in  the  body  are 
not  anatomically  distinguishable,  but  that  the  existence  of 
such  centers  and  such  nerves  is  based  wholly  upon  physio- 
logical grounds. 

QUANTITATIVE  DETERMINATIONS  OF  THE  SOURCE  AND  EXPEND- 
ITURE OF  HEAT. 

Heat  may  be  measured  just  as  corn  or  wheat.  The  unit 
of  heat  measure  is  called  the  calorie.  A  calorie  of  heat  is 
the  amount  of  heat  necessary  to  raise  the  temperature  of  one 
gram  of  water  from  zero  degrees  to  one  degree  C.  Or,  de- 
fining it  more  generally,  a  calorie  is  the  amount  of  heat  re- 
quired to  raise  one  gram  of  water  one  degree  C.  As  the 
amount  of  water  in  any  given  case  can  be  accurately  meas- 


382  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

ured,  and  as  the  temperature  may  be  equally  accurately 
measured  by  thermometers,  it  is  no  specially  difficult  task  to 
determine  quantitatively  the  amount  of  heat  under  investiga- 
tion. It  is  only  necessary  to  take  every  precaution  possible 
that  none  of  the  heat  shall  be  lost  by  radiation  or  convection, 
but  that  all  of  it  shall  be  transferred  to  a  known  quantity  of 
water  and  so  measured. 

Such  calori-metric  measurements  have  been  made  for  a 
number  of  substances  and  the  quantity  of  heat  which  they 
produce  in  burning  accurately  determined.  Thus,  one  gram 
of  carbon  produces  8,080  calories;  one  gram  of  hydrogen, 
34,460;  one  gram  of  proteids,  5,778;  one  gram  of  fat, 
9,372,  and  one  gram  of  sugar,  4,116  calories.  One  is  at 
first  astonished  at  this  stupendous  amount  of  heat.  On  the 
other  hand,  it  explains  easily  how  it  is  possible  for  a  body 
to  derive  all  its  energy  and  heat  from  comparatively  small 
amounts  of  proteids,  fats  and  sugars. 

To  the  older  investigators  it  seemed  impossible  that  the 
muscular  energy  and  the  large  amount  of  heat  lost  from  a 
living  body  should  all  be  derived  from  the  quantitatively 
small  amount  of  food  taken.  This  error  was,  however,  due 
to  their  ignorance  of  the  exact  amount  of  heat  which  even 
such  small  portions  of  food  produce  when  burned.  That 
this  amount  of  heat  seems  large  is  due  to  the  fact  that  in 
the  every  day  oxidations  of  the  physical  world  such  a  very 
large  proportion  of  the  heat  is  entirely  lost. 

THE  AMOUNT  OF  HEAT  LOST  BY  THE  BODY. 

Experiments  have  been  made  to  determine  the  amount 
of  heat  lost  by  the  human  body  in  a  day.  These  were  made 
by  placing  the  person  to  be  examined  in  a  close-jacketed 
calorimeter  so  that  all  the  heat  which  his  body  produced 
could  be  measured  by  measuring  the  temperature  of  the 
calorimeter  and  its  water  jacket.  The  experiment  was, 
practically  speaking,  to  confine  an  individual  in  a  relatively 
small  chamber,  or  still  better,  chest,  out  of  which  little  if 
any  heat  could  be  lost  by  convection  or  radiation.  The  re- 


THK  MAINTENANCE  OF  THE  ANIMAL  HEAT.     383 

suits  of  such  experiments  would,  of  course,  vary  largely  ac- 
cording to  the  nature  of  the  person  experimented  upon.  In 
a  person  resting,  about  2,500,000  calories  are  liberated  in 
one  day ;  or,  measuring  that  in  terms  of  the  water  which  it 
would  heat,  it  would  be  an  amount  of  heat  sufficient  to  raise 
56  pounds  of  ice  water  to  the  boiling  point.  These  figures 
are  materially  increased  for  a  day  of  regular  work.  In  a 
working  day  no  less  than  3,700,000  calories  are  produced. 
This  amount  of  heat  would  be  sufficient  to  raise  83  pounds 
of  water  from  the  freezing  to  the  boiling  point. 

These  figures  appear  at  first  startling  and  it  seems  almost 
incredible  that  in  one  day,  losses  so  large  should  occur. 
However,  the  fact  that  this  heat  is  being  continually  radi- 
ated little  by  little  explains  this  popular  error.  It  is  further 
interesting  to  know  that  the  amount  of  heat  lost  by  the  en- 
tire body,  plus  the  amount  of  energy  lost  in  muscular  motion, 
is  about  the  same  as  the  food  taken  during  the  day  would 
give  if  directly  oxidized  outside  of  the  body.  This  agree- 
ment between  the  theoretical  amount  of  heat  in  the  foods 
taken  and  the  actual  amount  of  heat  lost  in  the  body  when 
that  body  is  in  a  state  of  nutritive  equilibrium  proves  with- 
out further  question  the  source  of  all  the  energy  of  the  body 
and  the  absurdity  of  calling  in  any  so-called  vital  force  to 
explain  an  apparent  discrepancy. 

The  interesting  question  at  once  follows,  in  what  man- 
ner this  large  amount  of  heat  is  daily  lost  from  the  body. 
Here,  too,  fairly  accurate  experiments  help  us  out  and  show 
about  the  following  distribution  of  the  loss: 

73      per  cent,  direct  radiation  from  the  skin; 

i4*/2        "         evaporation  of  the  perspiration  from  the  skin; 

72Ao  from  the  lungs; 

35/io       "         in  the  warmth  of  the  expired  air; 

i8/io       "         lost  in  warming  the  excretions  of  the  body. 

It  was  pointed  out  in  a  previous  chapter  that  of  the 
available  energy  of  the  body  about  five-sixths  is  lost  in  heat, 
and  only  one-sixth  utilized  in  actual  muscular  movements. 
This  seems  a  very  heavy  proportion  of  loss  of  heat,  and  yet 


384  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

when  compared  with  the  best  engines  it  reveals  that  the 
body  is  very  much  superior  indeed  to  them  all.  It  is  a  very 
fine  engine  which  can  utilize  one-eighth  of  its  total  energy, 
while  most  ordinary  engines  utilize  no  more  than  from  one- 
tenth  to  one-twentieth.  As  the  workings  of  the  human 
body  are  subject  to  the  same  physical  laws  to  which  arti- 
ficial engines  are  subject,  it  reveals  the  marked  superiority 
of  the  body  with  reference  to  the  energy  at  its  disposal. 


CHAPTER  XVIII. 


THE  KIDNEYS,  THE    SKIN,  AND    THE   GENERAL 
PHYSIOLOGY   OF   EXCRETION. 

We  have  in  the  preceding  chapters  traced  the  foods 
through  the  various  changes  which  they  surfer  in  digestion ; 
they  have  been  followed  through  the  intestinal  walls  into 
the  blood  or  lymph  streams.  The  changes  which  some  of 
them  undergo  in  the  liver  has  been  explained.  We  have 
seen  them  distributed  in  the  blood  and  carried  to  the  indi- 
vidual tissues.  It  was  pointed  out  how  at  this  place  these 
foods  were  built  up  into  living  tissue,  and  how  by  the  dis- 
integration of  this  tissue  the  energy  was  produced.  There 
now  remains  the  final  question  concerning  the  nature  of  the 
waste  products  which  result  from  this  destruction  and  their 
final  elimination  from  the  body.  This  closing  chapter  in 
the  history  of  the  foods  and  tissues  has  therefore  to  do  with 
the  skin  and  the  kidneys,  the  organs  whose  duty  it  is  to 
take  the  final  products  of  metabolism  and  remove  them 
from  the  body. 

THE  KIDNEYS. 

The  kidneys  are  large,  bean  shaped  organs  lying  on  the 
back  wall  of  the  abdomen.  They  have  a  reddish  character- 
istic color,  but  are  usually  more  or  less  imbedded  in  con- 
nective or  adipose  tissue.  The  right  and  left  kidneys  do 
not  lie  at  the  same  level,  the  difference  in  position  between 
the  two  being  often  several  inches.  On  account  of  their 
proximity  to  the  back  wall  of  the  abdomen  pains  in  the 
kidneys  are  usually  referred  to  the  small  of  the  back.  A 
large  branch  from  the  aorta,  the  renal  artery,  carries  blood 
to  each  kidney,  and  a  corresponding  vein  carries  the  return- 
ing blood  to  the  ascending  vena  cava. 

25  (385) 


386 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


In  its  gross  structure  a  kidney  shows  a  connective  tissue 
covering  called  the  capsule.     The  kidney  itself  shows  two 


Ua, 


Fig.  127.— THE  URINARY  ORGANS  FROM  BEHIND.    (Henle.) 

A,  aorta;  Vc,  venacava;  Ar,  renal  artery;  Vr,  renal  vein ;  R,  right  kidney;  U,  ureter; 
Vu,  bladder;  Ua,  urethra. 

well  marked  areas,  an  outer  one,  reddish  in  appearance  in 
a  fresh  specimen,  and  somewhat  granular,   called  the   cor- 


KIDNEYS,    SKIN,    AND    GENERAL   EXCRETION. 


387 


.r,  and  an  inner  layer,  whitish,  revealing  numerous  glis- 
tening threads  running  towards  the  pelvis  of  the  kidney. 
This  second  area  is  called  the  medulla.  Between  the  cor- 
tex and  the  medulla  the  main  blood-vessels  of  the  kidney, 
both  arteries  and  veins  take  their  course.  The  interior  of 
the  kidney  is  hollow,  and  is  called  the  pelvis.  This  pelvis 
connects  with  the  ureter,  by  means  of  which  duct  the  se- 
cretion is  carried  to  the  bladder.  The  medulla  breaks  in 
the  pelvis  into  several  (five  to  ten)  pyramidal  projections, 
called  the  pyramids  of  Malpighi.  At  the  ends  of  these 


Fijf.  128.— DIAGRAMMATIC  SECTION  THROUGH  PART  OF  KIDNEY  PARALLEL  TO  TUBULES. 

(After  Testut.) 

ff,  papilla;  b,  medulla;  c,  cortex;  2,  capsule;  3,  tubules  in  medulla;  4,  blood-vessels; 
9,  Malpighian  corpuscles. 

pyramids  numerous  uriniferotis  tubules  open  into  the  pelvis. 
The  depressions  between  the  pyramids  are  called  the 
calyces. 


388  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

All  the  points  so  far  could  easily  be  made  out  on  a  kid- 
ney without  the  use  of  any -lens.  For  the  final  structure, 
the  courses  of  the  blood-vessels  and  the  uriniferous  tubules, 
recourse  must  be  had  to  histological  sections.  For  the  sake 
of  clearness  it  may  be  advisable  to  follow  at  first  the  course 
of  the  blood-vessels  for  some  distance  without  paying  atten- 
tion to  other  structures,  and  then  to  turn  to  the  uriniferous 
tubules. 

1. — The  Circulation  of  Blood  Through  the  Kidneys. 
The  renal  artery  enters  the  kidney  at  the  hilum,  and  at  once 
divides  into  numerous  branches  which  run  in  every  direc- 
tion between  the  cortex  and  the  medulla.  From  these  main 
branches  there  arise  smaller  ones,  which  run  directly  out- 
wards through  the  cortex  to  the  capsule.  These  branches 
in  turn  divide  into  shorter  branches,  and  these  short 
branches  soon  terminate  each  in  a  small  knot  of  blood- 
vessels, giving  to  the  whole  the  appearance  of  a  bunch  of 
grapes.  This  network  of  blood-vessels  is  not  really  a 
capillary  network.  It  is  rather  a  nodule  of  small  twisted 
arteries,  with  walls,  however,  sufficiently  thin  to  allow  the 
water  and  the  salt  of  the  circulating  blood  to  pass  out  at 
this  point  somewhat  readily.  It  is,  therefore,  well  to  bear 
in  mind  that  the  blood  as  it  re-issues  from  this  knot  is  still 


Fig.  129.— A,  SHOWING  THE  RELATIONS  OF  THE  BLOOD-VESSELS  AND  URINIFEROUS  TU- 
BULE; B,  A  SINGLE  GLOMERULUS  FROM  A  PIG'S  KIDNEY.  (After  Bowman  and  Lud- 
wig.) 

arterial.     Upon  leaving  this  knot,  called  a  Malpighian  cor- 
puscle or  glomerulus,  the  artery  soon  divides  into  capillar- 


KIDNEYS,    SKIN,    AND    GENERAL   EXCRETION.  389 

ies  which  surround  in  a  very  intricate  way  the  uriniferous 
tubules  lying  in  the  cortex.  It  is  at  this  point  that  the  real 
secretion  of  the  kidney  takes  place.  After  having  passed 
from  the  capillaries  it  is  gathered  up  in  veinlets,  which 
carry  the  blood  back  to  the  larger  veins  lying  between  the 
cortex  and  the  medulla,  which  in  turn  unite  at  the  hilum 
and  leaving  the  kidney  form  the  renal  vein. 

The  circulation  through  the  medulla  is  much  simpler. 
Small  arteries  run  inward  from  the  main  branches  between 
the  cortex  and  medulla,  and  divide  up  into  capillaries 
which  there  surround  the  uriniferous  tubules,  while  corre- 
sponding veins  collect  this  blood  and  carry  it  back  to  the 
larger  veins  lying  between  the  cortex  and  medulla,  where  it 
joins  the  regular  venous  stream.  The  circulation  of  the 
blood  from  the  medulla  is  for  nutritive  purposes  only,  and 
no  active  secretion  takes  place  here.  The  real  physiology 
of  the  kidney  belongs  to  the  cortex. 

2. — The  Course  of  the  Uriniferous  Tubule.  It  was 
just  pointed  out  that  from  the  main  arteries  lying  between 
the  cortex  and  medulla  smaller  arteries  ran  directly  out- 
wards through  the  cortex  towards  the  capsule;  that  these 
arteries  gave  off  a  number  of  lateral  branches,  and  that  these 
lateral  branches  soon  ended  in  arterial  knots  called  the 
Malpighian  corpuscles,  but  that  the  blood  reissued  from 
these  knots  still  arterial  and  then  divided  up  into  capillar- 
ies surrounding  the  uriniferous  tubules.  It  now  remains  to 
trace  with  reference  to  this  course  for  the  blood,  the  course 
of  the  secreting  tubules. 

The  secreting  or  uriniferous  tubules  are  very  long  tubes 
intricately  folded  and  bent  and  form  almost  all  of  the  re- 
maining portion  of  the  cortex.  Each  uriniferous  tubule  be- 
gins as  a  sac-like  dilatation  surrounding  a  Malpighian  cor- 
puscle and  forms,  so  to  speak,  the  capsule  around  these 
corpuscles.  The  blood-vessels,  however,  do  not  really  lie 
inside  of  this  dilatation,  but  as  in  the  case  of  the  heart  and 
pericardium,  folded  in  by  a  reduplication  of  the  wall.  It  is 


390 


STUDIES    IN   ADVANCED    PHYSIOLOGY. 


at  this  point  that  almost  all  of  the   water  of   the  secretion 
finds  its  way  unto  the  uriniferous  tubnles. 

This  dilatation  connects  with  the  regular  tubular  portion 
of  the  duct.  The  portion  immediately  following  the  dilata- 
tion is  called  the  neck.  Beyond  the  neck  the  tubule  be- 
comes somewhat  convoluted,  and  is  spoken  of  as  the  first 
convoluted  tubule.  It  then  descends  abruptly  through  the 
cortex  down  into  the  medulla,  this  portion  being  called  the 
descending  limb  of  Henle.  In  the  medulla  it  makes  a  sharp 
turn,  called  the  loop  of  Henle  and  then  ascends  again 
through  medulla  and  cortex  to  almost  the  point  of  begin- 
ning, this  ascending  portion  being  called  the  ascending 
limb  of  Henle.  It  then  usually  bends  and  runs  back  almost 
to  its  Malpighian  corpuscle,  this  portion  being  called,  be- 
cause of  its  convoluted  nature,  the  second  convoluted 
tubule.  Near  its  Malpighian  body  it  makes  a  sharp  turn 
again,  flowing  in  an  opposite  direction,  and  on  account  of 


Fig.   130.— DIAGRAM   SHOWING   THE   COURSE   OF   TWO   URINIFEROUS   TUBULES.     (After 
Klein.) 

A,  cortex;  B,  medulla;  C,  papilla;  a,  a',  regions  free  from  glomeruli. 
For  meaning  of  numbers  see  text. 

the  somewhat  angular  turns  is  called  the  zig-zag  tubule. 
This  zig-zag  tubule  soon  leads  into  one  of  the  large  collect- 


KIDNEYS,    SKIN,    AND    GENERAL    EXCRETION.  391 


ing  tubules,  into  which  other  zig-zag  tubules  enter,  and  by 
means  of  this  large  collecting  tubule  which  runs  from  cor- 
tex and  medulla,  the  secretion  is  finally  poured  into  the 
pelvis  of  the  kidney.  These  large  collecting  ducts  are 
called  the  ducts  of  Bellini.  The  whitish  glistening  threads 
so  characteristic  of  the  medulla  are  such  ducts  of  Bellini. 
The  course  of  the  uriniferous  tubule  as  just  given  permits, 
of  course,  of  certain  variations,  but  is  with  a  surprising 
regularity  the  usual  one. 

Most  of  the  cortex  and  even  some  of  the  upper  portions 
of  the  medulla  consists  of  these  closely  packed  tubules  with 
their  accompanying  blood-vessels.  On  cross  sections  each 
tubule  shows  a  single  layer  of  columnar  epithelial  cells  rest- 
ing on  a  small  basement  membrane,  and  it  is  these  epithelial 
cells  which  play  the  physiological  role  of  the  kidney.  It  is 
these  cells  which  pick  out  of  the  blood  the  nitrogenous 
waste  products  and  pass  them  into  their  lumen.  At  the 


Fig.  131.— TUBULES  FROM  A  SECTION  OF  THE  DOG'S  KIDNEY.     (After  Klein  and  Noble 

Smith.) 

a,  capsule,  enclosing  glomerulus;  n,  neck;  c,  c,  convoluted  tubules;  /,  from  the  limb 
of  Henle  (in  the  medulla) ;  d,  a.  collecting  tubule. 

Malpighian  corpuscle,  that  is,  at  the  very  head  of  the  urin- 
iferous tubule,  water,  and  some  salts  of  course,  are  -being 
continually  poured  into  the  tubule,  and  this  stream  serves 
to  wash  out  other  substances  passed  into  it.  The  fact  that 
urea  and  many  other  nitrogenous  compounds  are  with  diffi- 
culty soluble  in  water  at  ordinary  temperatures  accounts  for 
the  large  volume  of  water  required  by  the  kidney  to  wash  out 
this  product.  We  have  therefore  to  look  upon  the  function 


392  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

of  the  Malpighian  corpuscles  of  the  cortex  as  mechanical 
rather  than  physiological,  serving  merely  as  flush  basins  at 
the  top  of  the  tubule  to  keep  this  lumen  perfectly  clear  of 
obstructions,  while  the  cells  that  line  the  tubule  are  the 
physiological  agents  directly  concerned  in  picking  out  of  the 
blood  the  waste  products  in  question. 

It  may  be  well  to  repeat  at  this  point  the  fact  that  these 
nitrogenous  products  are  not  formed  by  the  kidney  at  all. 
Derived  in  the  form  of  kreatin  or  kreatinin,  or  similar  sub- 
stances from  the  breaking  down  of  the  tissues,  they  are  car- 
ried to  the  liver  and  there  changed  to  urea  and  its  kindred 
compounds,  from  which  place  by  means  of  the  regular  blood 
stream  they  reach  the  kidney,  and  in  this  organ  are  merely 
picked  up  by  the  tubular  epithelium  and  eliminated.  It 
must  not,  however,  be  supposed  that  this  elimination  of  the 
nitrogenous  products  is  a  mere  physical  filtration.  It  is  an 
active  physiological  process,  depending  upon  the  vital 
energy  of  the  epithelial  cells  that  line  the  tubules.  It  is  due 
to  the  special  activity  of  these  cells  that  these  waste  pro- 
ducts are  removed,  and  that  many  other  almost  equally  di- 
alyzable  substances  are  not  permitted  to  pass  through.  In 
cases  of  inflammation,  or  in  cases  of  the  more  or  less  gen- 
eral disintegration  of  these  epithelial  cells,  other  substances 
do  pass  into  the  secretion  and  such  diseases  as  diabetes  or 
Bright 's  disease  are  the  result. 

The  elimination  of  the  water  and  salt  in  the  glomeruli 
or  the  Malpighian  corpuscles,  is  to  a  very  large  extent  a 
physical  process.  This  is  proved  by  the  fact  that  the  amount 
of  such  water  and  salt  eliminated  from  the  kidney  is  to  some 
extent  directly  proportional  to  the  amount  of  blood  which 
passes  through  the  kidney  and  to  the  arterial  pressure  in  the 
kidney,  hence  any  rise  in  arterial  pressure  or  any  increase 
in  the  swiftness  of  the  blood  stream  will  usually  reveal  itself 
in  an  increased  secretion  from  that  organ.  That  it  is 
nothing  but  a  physical  filtration  is  not  claimed.  In  fact,  it 
is  probable  that  even  the  lining  cells  of  the  corpuscle  exert 
a  physiological  action. 


KIDNEYS,    SKIN,    AND    GENERAL   EXCRETION.  393 

That  the  phenomena  of  secretion  are  controlled  by  nerves 
is  evident  for  several  reasons.  States  of  the  emotions,  ex- 
cessive pain,  may  affect  the  amount  of  such  secretion 
through  this,  innervation.  It  has,  however,  not  been  possi- 
ble so  far  to  trace  these  nerves  to  their  final  terminations. 
There  is  no  objection,  though,  against  believing  that  these 
nerves  end  in  or  near  the  epithelium  cells  of  the  tubules  and 
capsule,  and  that  the  increased  or  decreased  secretion  is  not 
wholly  due  to  vascular  changes.  A  number  of  drugs  known 
as  diuretics  affect  the  kidneys,  causing  an  increase  in  its  se- 
cretion, but  whether  due  to  vascular  changes  or  to  a  direct 
stimulus  of  the  secreting  cells  is  not  clear. 

THE  KIDNEY  SECRETION. 

The  amount  of  urine  eliminated  in  one  day  is  about 
1,600  grams.  Its  specific  gravity  is  1,020,  that  is,  slightly 
heavier  than  water.  Its  composition  consists  of  96  per  cent. 
water  and  4  per  cent  solids.  These  4  per  cent,  solids  are: 

(1)  Urea  and  its  derivatives;  uric  acid,  kreatin  and  xan- 
thin. 

(2)  Aromatic  bodies  such  as  hippuric  acid,  kresol,  indol, 


(3)  Oxalic  acid  in  the  form  of  calcium  oxalate. 

(4)  Pigments. 

(5)  Mineral   salts;    sodium   chloride,   phosphates   and 
sulphates  of  potassium,  calcium,  magnesium,  ammonia  in 
the  form  of  urate.     In  addition  to  these  solids  slight  quan- 
tities of  CO2  are  dissolved  in  the  liquid. 

The  most  important  of  these  solid  bodies  is  the  urea.  Its 
chemical  composition  is  given  in  the  formula  CO  (NH2)2- 
It  is  the  final  product  of  nearly  all  the  albumens  and  albu- 
minoids which  have  been  used  up  in  the  tissues.  It  is, 
therefore,  the  substance  in  which  the  nitrogen  of  the  foods 
is  eliminated.  Reference  to  the  chemical  formula  will  show 
that  it  contains  a  relatively  large  amount  of  nitrogen. 
This  substance  is  interesting  as  having  *been  the  first  or- 
ganic substance  which  was  produced  artificially  in  the  la- 


394  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

boratory.  In  1828  the  chemist  Wohler  discovered  that  by 
allowing  a  solution  of  ammonium  cyanate  (NH4  CON)  to 
stand  exposed  to  the  air  it  changed  into  urea  CO  (NH2)2. 

It  will  be  noticed  in  comparing  the  chemical  composi- 
tions of  these  two  substances  that  they  have  the  same  rela- 
tive number  of  atoms.  Urea  is,  therefore,  but  a  re-arrange- 
ment of  the  molecular  structure  of  ammonium  cyanate.  It 
was,  of  course,  easy  to  make  ammonium  cyanate  out  of  its 
elements  in  the  laboratory,  and  so  it  became  possible  to 
make  urea  artificially  in  the  chemist's  retorts.  Before  this 
time  it  had  been  believed  without  question  that  all  organic 
compounds,  that  is,  compounds  made  by  plants  or  animals, 
differed  essentially  from  compounds  made  artificially.  It 
was  believed  that  in  the  construction  of  organic  compounds 
vital  forces  were  at  work  in  addition  to  chemical  affinities. 
This  wonderful  discovery  at  once  showed  the  error  of  this 
view  and  opened  the  way  for  the  increased  study  of  organic 
compounds  and  for  the  artificial  manufacture  of  innumera- 
ble ones  now  on  the  markets.  It  was  the  first  blow  to  break 
down  the  distinction  between  organic  and  inorganic  chem- 
istry. 

This  urea  may  be  extracted  from  tne  secretion  in  a  pure 
solid  form.  It  crystallizes  in  white  four-cornered  prisms,  or 
when  crystallized  very  rapidly,  in  fine  needles.  The  solid 
crystals  are  soluble  in  water,  alcohol,  and  many  other  solu- 
tions, but  are  perfectly  insoluble  in  ether. 

If  a  solution  containing  urea  be  allowed  to  stand  for  some 
time  exposed  to  the  air,  it  ferments  under  the  action  of 
germs  falling  into  it  from  the  air,  and  the  urea  uniting 
chemically  with  some  of  the  water  changes  into  ammonium 
carbonate.  This  change  is  called  the  fermentation  of  the  urea. 
Ammonium  carbonate,  more  familiar  as  the  salts  of  harts- 
horn, has  its  peculiar  characteristic  odor,  and  it  is  to  this 
substance  that  the  odor  of  fermented  urine  is  due. 

The  derivatives  of  urea,  such  as  uric  acid,  kreatin,  xan- 
thin  and  others,  are  found  in  relatively  small  amounts.  Under 
certain  conditions,  however,  the  uric  acid  may  accumulate 


KIDNEYS,    SKIN,    AND    GENERAL   EXCRETION.  395 

in  the  body,  and  acting  as  a  poison  deposited  usually  in  the 
joints,  give  rise  to  the  familiar  symptoms  of  gout  and  kin- 
dred diseases. 

The  aromatic  bodies,  such  as  hippuric  acid,  kresol,  in- 
dol  and  skatol  are  found  in  very  small  quantities.  Hippuric 
acid,  however,  occurs  in  relatively  very  large  amounts  in 
the  renal  secretion  of  herbivorous  animals.  The  kresol,  in- 
dol  and  skatol  are  substances  which  have  resulted  from  the 
disintegration  of  albumens  in  the  intestine,  but  having 
been  absorbed  by  the  blood  are  eliminated  again  through 
the  kidneys. 

The  characteristic  color  of  the  renal  secretion  is  due  to 
a  number  of  pigments.  The  best  known  of  these  is  the 
pigment  known  as  uro-bilin.  This  uro-bilin  is  probably  de- 
rived from  the  same  source  as  the  bilirubin  of  the  bile,  that 
is,  from  the  disintegration  of  red  corpuscles,  or  more  ex- 
actly, from  the  haemoglobin  of  red  corpuscles. 

The  mineral  salts  include  a  number  of  mineral  sub- 
stances which  are  the  products  of  tissue  disintegration,  but 
in  addition  excesses  of  salts  which  have  been  directly  elim- 
inated from  the  blood.  Experiments  show  that  when  cer- 
tain mineral  salts  in  increased  quantities  reach  the  blood 
they  are  at  once  eliminated  in  this  manner.  On  this  account 
the  eating  of  even  excessive  amounts  of  salt  has  no  directly 
injurious  effect  whatever  upon  the  body. 

It  is  sometimes  of  the  utmost  importance  to  the  physi- 
cian to  be  able  to  determine  the  composition  of  urine,  espe- 
cially when  the  presence  of  sugar  or  albumen  is  suspected. 

Quite  a  large  additional  number  of  chemical  substances 
occur  in  more  or  less  minute  quantities  in  the  secretion,  but 
the  nature  of  these  substances  from  a  chemical  standpoint 
is  so  complicated,  and  in  the  real  physiology  of  the  body 
they  play  such  an  unimportant  role  that  in  this  discussion 
they  are  omitted  altogether. 

By  way  of  summary  it  may  be  stated  then  that  the  real 
significance  of  the  physiology  of  the  kidney  lies  in  its 
power  to  eliminate  superfluous  or  injurious  substances, 


396  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

and  to  rid  the  body  of  the  nitrogenous  products  resulting 
from  the  metabolism  of  the  tissues.  The  kidneys  are  able, 
when  necessary,  to  eliminate  hurriedly  accidentally  received 
substances,  such,  for  instance,  as  poisons  of  one  kind  or 
another,  and  so  prevent  the  liability  of  injury  from  them. 
This  no  doubt  explains  the  power  of  the  body  to  recover 
from  such  poisonings. 

While  most  of  the  work  of  secretion  thus  devolves  upon 
the  kidneys,  they  are  able  to  be  relieved  in  part  by  the  skin, 
which,  in  addition  to  its  functions  as  a  protection  to  the 
body,  serves  quite  materially  in  a  manner  similar  to  that  of 
the  kidney,  and  in  cases  where  the  kidneys  have  been  over- 
worked and  have  lost  some  of  their  vitality,  assumes  this 
extra  duty.  On  the  other  hand,  when  the  skin  for  some 
reason  is  prevented  from  exercising  this  excretory  function 
an  unnaturally  increased  amount  of  work  is  thrown  upon 
the  kidneys. 

THE    SKIN. 

The  covering  of  the  body,  or  the  skin,  consists  of  two 
essentially  different  layers ;  an  outer  layer  made  up  of  cells 
entirely,  called  the  cuticle  of  epidermis,  and  an  inner  layer 
consisting  almost  wholly  of  connective  tissue  fibers,  with 
contained  blood-vessels,  glands,  nerves  and  so  on,  called 
the  corium  or  cutis-vera,  that  is,  true  skin. 

1. — Epidermis.  The  epidermis  is  a  stratified  epithelium 
composed  wholly  of  epithelial  cells.  These  cells  are, 
however,  not  all  alike,  the  cells  of  the  deeper  layers,  next 
to  the  cutis-vera,  being  more  cuboidal  in  shape  than  the 
flattened  and  dead  cells  forming  the  horny  covering  at  the 
surface.  The  gradation  from  these  dead  flattened  cells  on 
the  outside  to  the  living  cuboidal  cells  next  to  the  corium  is 
tolerably  gradual.  The  lowest  layer  of  cells,  that  immedi- 
ately in  contact  with  the  corium,  is  called  the  Malpighian 
layer  of  the  epidermis.  It  consists  of  well-marked  nucle- 
ated cells  of  pronounced  cuboidal  form.  It  is  these  cells 
which  by  their  division  give  rise  to  all  of  the  remaining 
cells  of  the  epidermis.  The  cells  of  this  Malpighian  layer 


KIDNEYS,    SKIN,    AND    GENERAL   EXCRETION. 


397 


divide,  and  thus  the  top  layers  of  the  epidermis  are  being 
continually  pushed  further  and  further  out  by  the  addition 


Fig.  132.— SECTION  OF  SKIN  AJO>  SUBCUTANEOUS  TISSUE.    (After  Kolliker.) 
a,  horny  layer;   b,  Malpighian  layer  of  epidermis;   c,  corium;   rf,  subcutaneous  fatty 
tissue;  e,  papillae;  f,  fat;  g,  sweat  gland;  h,  duct;  i,  mouth  of  sweat  gland. 

of  new  cells  from  beneath.  The  layers  of  these  derived 
cells,  lying  close  to  the  Malpighian  layer,  also  resemble 
the  Malpighian  layer  in  having  well-defined  nuclei  and 
in  their  cuboidal  shape.  But  further  outward  a  chem- 
ical change  sets  in,  by  means  of  which  the  substance 
of  these  cells  seems  changed  into  a  horny  material  akin 
to  the  keratin  of  ordinary  horns,  while  in  addition  to 
this  chemical  change  they  become  more  and  more  flattened, 
losing  more  and  more  the  appearance  of  cells  until  at  the 
top  of  the  epidermis  they  occur  as  mere  horny  scales,  which 
from  time  to  time,  by  contact  with  other  bodies  or  by  the 
friction  of  towel,  etc.,  are  broken  off  from  the  skin. 

The  layer  of  the  epidermis  in  which  this  chemical  change 
takes  place  is  readily  visible  in  sections  as  much  clearer 
looking,  due  to  the  fact  that  the  cells  have  undergone  a 
transformation  into  the  somewhat  transparent  horny  ma- 


398  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

terial.     For   this    reason    it    has    been  termed  the  stratum 
lucidum. 

It  will  therefore  be  observed  that  the  epidermis  is  not  at 
all  in  any  way  derived  from  the  dermis  beneath.  The  der- 
mis  is  fibrous,  the  epidermis  cellular.  The  epidermis  is 
a  result  of  the  continued  division  of  the  Malpighian  layer 
of  the  epidermis,  and  when  this  layer  is  not  present,  as  in 
serious  wounds,  scalds  or  bruises,  it  is  absolutely  impossi- 
ble for  the  epidermis  to  appear.  Under  such  conditions  at- 
tempts are  frequently  made  to  graft  portions  of  the  Mal- 
pighian layer  from  another  body  on  to  this  spot,  and  if  the 
graft  is  successful  the  epidermis  begins  to  grow  from 
these  places  by  the  proliferation  of  the  Malpighian  cells  en- 
grafted. These  Malpighian  cells  are  further  of  interest  in 
the  fact  that  in  them  lie  the  pigments  which  characterize 
the  various  races  of  mankind.  A  certain  amount  of  pig- 
ment also  occurs  in  the  cells  above  the  Malpighian  layer, 
but  it  is  much  less  pronounced,  and  the  intense  black  of  the 
colored  races,  or  the  red  of  the -Indian  is  the  color  which 
shines  through  the  somewhat  transparent  epidermis  from  the 
Malpighian  layer  at  its  base. 

2. — Corium.  The  corium  or  true  skin  is  the  fibrous 
part  of  the  skin  lying  immediately  beneath  the  epidermis. 
It  consists  almost  wholly  of  closely  packed  white  fibrous 
tissue,  containing,  however,  a  small  amount  of  yellow  elas- 
tic fibers.  In  the  meshes  of  these  fibers  are  found  con- 
nective tissue  corpuscles,  imbedded  nodules  of  fat,  blood- 
vessels and  nerves,  and  finally  the  glands  of  the  skin. 

The  true  surface  of  the  corium  is  thrown  up  into  pecu- 
liar papillae  sometimes  simple,  sometimes  branched,  which 
project  up  into  the  epidermis.  In  these  papillae  thert  lie 
in  some  instances  loops  of  blood-vessels,  more  generally 
tactile  corpuscles  concerned  in  the  sense  of  touch.  These 
papillae  are  arranged  in  defined  rows,  and  as  the  epidermis 
follows  these  papillae  they  show  on  the  outside  of  the  skin 
as  those  peculiar  lines  and  furrows  so  evident  on  the 


KIDNEYS,    SKIN,    AND    GENERAL    EXCRETION.  399 

fingers  and  the  palm  of  the  hand.     These  furrows  are  prob- 
ably not  alike  in  any  two  individuals .      When  once  formed 


Fig.  133.— SECTION  OF  THE  HUMAN  EPIDERMIS,  SHOWING  TWO  VASCULAR  PAPILLA  BE- 
NEATH.    (After  Heitzmann.) 
BP,  loop  of  capillaries;  Dp,  duct  of  sweat  gland;  EB  horny  layer  of  epidermis;  PL, 

stratum  lucidum;   V,  Malpighian  layers  of  epidermis. 

they  never  change,  the  impressions  of  the  furrows  on  an 
infant's  thumb  being  identical  with  the  impression  of  the 
same  thumb  in  old  age.  In  some  countries  impressions  are 
made  of  the  furrows  of  the  fingers  or  thumbs  of  criminals 
in  order  that  they  may  keep  a  perfectly  trustworthy  de- 
scription of  them,  it  being  impossible  for  the  criminal  to 
change  this  part  of  his  personal  appearance.  The  absolute 
correspondence  of  an  impression  so  taken  at  any  time  and 
the  thumb  offered  in  evidence  would  be  incontrovertible 
proof  of  the  identity  of  the  man.  These  papillae  while 
present  over  nearly  all  portions  of  the  skin  are  especially 
plentiful  in  those  portions  of  the  body  where  the  sense  of 
touch  is  peculiarly  acute. 

Through  the  corium  run  the  blood-vessels,  veins  and 
capillaries.  The  epidermis  has  no  direct  vascular  supply, 
although  the  tips  of  capillary  loops  do  sometimes  reach 
slightly  beyond  the  Malpighian  layer.  The  epidermis  is 
therefore  obliged  to  draw  its  nourishment  from  the  lymph 


400 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


distributed  beneath  it.  This  is,  of  course,  in  accordance 
with  the  common  observation  that  blood  is  not  drawn  as 
long  as  the  cut  is  confined  to  the  cuticle. 

Nerves  also  traverse  the  corium  and  are  distributed  to 
the  contained  blood-vessels  and  glands,  while  the  special 
nerves  of  touch  end  in  the  touch  corpuscles.  Small  rami- 
fications of  nerves  penetrate  the  epidermis  and  run  in 
among  the  epithelial  cells,  ending  usually  between  these  in 
little  knob-like  swellings,  or  terminating  in  certain  espe- 
cially modified  cells  which  have  been  interpreted  as  sensory 
cells  in  the  epidermis.  A  detailed  description  of  these  cells 
and  the  touch  corpuscles  is  reserved  for  the  chapter  on  the 
4 ' Special  Senses." 


Fig.  134.— SBCTION  OF  THE  SKIN  SHOWING  TWO  PAPILLA.     (After  Biesiadecki.) 
a,  vascular  papilla,  containing  a  capillary  loop  from  the  artery  c;   fc,  sense  papilla, 

containing  a  tactile  corpuscle  t;   d,f,f,  three  nerve  fibers,  running  to  and  around  the 

papilla. 

The  corium  is  held  to  the  underlying  tissues  by  a  loose 
coat  made  up  almost  wholly  of  connective  tissue  fibers. 

In  some  places  this  binding  coat  is  rather  poorly  de- 
veloped, leaving  the  skin  loose  and  giving  it  much  latitude 
of  movement. *  In  others  the  skin  is  bound  firmly  down  to 


KIDNEYS,    SKIN,    AND    GENERAL    EXCRETION.  401 

the  flesh  and  the  transition  from  the  skin  is  so  gradual  as  to 
be  indeed  difficult  to  follow.  The  fibrous  nature  of  the 
corium  may  be  a  matter  of  easy  observation  on  any  piece  of 
leather,  a  torn  edge  here  displaying  frequently  very  satis- 
factorily the  tanned  shreds  of  fibers  which  go  to  make  up 
the  material.  The  process  of  tanning  consists  in  nothing 
more  than  taking  plexuses  of  connective  fibers,  forming  the 
corium  or  true  skin,  and  treating  these  with  a  substance 
called  tannin,  by  means  of  which  they  are  hardened  and 
transformed  into  a  substance  which  increases  their  strength 
as  well  as  their  resistance  to  decay.  It  need  not  be  added 
that  the  epidermis  does  not  figure  at  all  in  this  process. 

SPECIAL  MODIFICATIONS  OF  THE  EPIDERMIS. 

1. — Nails.  The  epidermis  is  in  certain  portions  of  the 
body  specially  modified  to  form  hairs  or  nails.  A  nail  is  a 
portion  of  very  much-thickened  epidermis,  the  component 
cells  of  which  are  much  more  closely  packed,  and  the  chem- 
ical change  of  which  into  keratin  or  horn  is  more  complete. 
The  posterior  part  of  a  nail  is  concealed  in  a  groove  of  the 
skin,  and  it  is  at  this  point  that  the  nail  increases  in  length 
by  the  formation  of  new  epithelial  cells.  The  nail  grows  in 
thickness  by  the  proliferation  of  cells  from  the  bed  of  the 
nail,  the  thickest  portion  of  the  nail  being  the  exposed  end. 
The  nail  usually  presents  near  its  root  a  lens-shaped  white 
area  known  as  the  lunula.  This  whitish  appearance  is  due 
to  an  opacity  at  this  point,  resulting  from  the  thickness  of 
the  nail  bed  immediately  under  it,  the  cells  of  which  are  in 
very  active  division  to  increase  the  thickness  of  the  nail. 
The  cells  of  the  root  and  bed  of  the  nail,  in  active  process 
of  division  are  soft,  while  those  longest  formed  and  next  the 
surface  or  end  of  the  nail  are  in  increasing  degrees  horny, 
differing,  however,  from  the  horny  cells  of  the  ordinary 
epidermis  in  the  fact  that  they  seem  to  possess  spiny  pro- 
cesses, by  means  of  which  they  are  firmly  interlocked  and 
united. 
26 


402  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

That  the  nail  is  an  epidermal  structure  is  not  only 
proved  from  its  composition  of  epidermal  cells,  but  also 
proved  by  the  source  from  which  the  root  of  the  nail  is  de- 
rived. In  very  early  life,  as  early  as  the  third  month  of 
uterine  life,  the  epidermis  at  the  point  where  the  root  of 
the  nail  is  to  form  bends  inward  forming  a  groove,  which 
groove  finally  imbedded  in  the  deeper  layers  of  the  skin  be- 
comes the  matrix  for  the  growing  nail.  It  is  said  that  the 
continued  rate  of  growth  of  a  nail  is  about  one-thirtieth  of 
an  inch  per  week.  As  in  case  of  epidermis  in  any  part  of 
the  skin  a  new  nail  is  able  to  appear  only  when  in  the  pull- 
ing away  of  the  old  one  the  deeper  layers,  the  Malpighian 
layers,  of  the  nail  root  are  left  intact. 

2. — The  Hair.  A  second  modification  of  the  epidermis 
is  the  hairs.  They  appear  about  the  third  or  fourth  month 
of  embryonic  life  as  growths  from  the  Malpighian  layer  down 
into  the  deeper  parts  of  the  corium.  This  ingrowth  soon 
divides  into  an  outer  wall  of  epidermal  tissue  which  becomes 
the  wall  of  the  hair  follicle,  and  an  inner  portion  which 
appears  as  the  hair.  The  growing  portion  of  the  hair  is  at 
the  bottom  of  the  hair  follicle  where  the  Malpighian  cells 
are  in  constant  process  of  division.  This  point  of  growth  is 
spoken  of  as  the  root  of  the  hair,  and  on  account  of  the 
continued  proliferation  of  new  cells  is  highly  vascular. 
These  blood-vessels  really  lie  in  the  corium,  but  the  corium 
at  this  point  usually  extends  some  distance  into  the  hair 
root,  like  a  papilla,  on  which  and  around  which  the  dividing 
cells  of  the  hair  root  are  placed.  At  the  root  the  cells  which 
go  to  make  up  the  shaft  of  the  hair  are  more  or  less  alike, 
but  a  differentiation  at  once  begins,  and  along  the  shaft 
proper  the  following  structure  of  the  hair  may  be  easily 
made  out  with  the  microscope. 

Surrounding  the  hair  is  a  single  layer  of  flattened  cells 
forming  a  kind  of  scaly  covering.  This  is  called  the  hair 
cuticle.  Beneath  this  thin  cuticle  is  the  real  fibrous  por- 
tion of  the  hair.  In  most  hairs  this  fibrous  portion  consti- 


KIDNEYS,    SKIN,    AND    GENERAI,   EXCRETION. 


403 


tutes  the  entire  remainder  of  the  shaft.  It  consists  of  deli- 
cate fibers  closely  packed  together,  running  of  course  in  the 
longitudinal  direction  of  the  shaft.  Finer  investigation  re- 
veals that  these  fibers  are  in  turn  com- 
posed of  flattened  and  elongated  cells. 
On  these  dried  and  elongated  cells  rem- 
nants of  nuclei  may  sometimes  be  still 
visible.  In  the  cells  that  make  this 
fibrous  portion  there  is  a  deposit  of  pig- 
ment to  which  the  hair  in  question  owes 
its  color.  In  older  hairs  air  spaces  may 
arise  by  a  kind  of  drying  process,  which 
by  their  reflection  of  the  light  give  to 
the  hair  a  grayish  appearance.  Such 
hairs,  when  soaked  in  certain  liquids 
become  entirely  transparent,  these  air 
spaces  being  filled  up  with  the  liquid  in 
question,  but  when  the  hair  is  again 
dried  the  liquid  evaporates,  the  air  again 
enters  these  spaces  and  the  old  color  re- 
appears. It  is  said  by  some  observers 
that  the  pigment  of  the  hair,  be  it 
black,  brownish  or  reddish,  is  carried  to 
the  cells  at  the  root  of  the  hair  by  pe- 
culiar wandering  pigment  cells  reach-  Fig 
ing  it. 

In  some  cases  the  interior  of  the  hair      a>  mouth  of  follicle.   6f 
is  occupied  with  a  kind  of  medulla  or  neck;  c' root;  ^^  coats  of 

/.     .  .  the  dermis;  /,  g,  outer  and 

pith.       ThlS  pith  IS   COmpOSed  Of  rOWS  Of   inner  root  sheathes  of  epi- 

cells  of  a  generally  angular  form.     It  is  hal^i.^kh-ThaT^; 
especially  apt   to    appear  in  advancing  m>  fat;  n,  an-ector  muscle; 

.     f  ,   .  .,..  o,   papilla  of  cuds;   s,  Mal- 

years,  and  the  whiteness  of  hair  is  usu-  Pighian  layer;  «,  sebaceous 
ally  due  to  the  contained  air  which  lies  glands- 
in  the  spaces  among  these  cells,  and  in  some  instances  ac- 
tually in  the  cells.  These  air  spaces  are  of  course  pro- 
duced by  the  drying  of  the  hair  in  its  exposure  to  the 
atmosphere. 


,IN 
LONGITUDINAL      SECTION. 

(After  Biesiadecki.) 


404  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

On  cross  sections  the  shaft  of  the  hair  is  usually  round. 
In  some  individuals,  however,  and  in  certain  races  it  is 
more  regularly  flattened.  Such  hairs  show  a  natural  tend- 
ency to  curl  on  account  of  the  unequal  growths  at  the  different 
angles.  The  size  of  these  hair  shafts  is  also  a  racial  char- 
acteristic. It  is  rather  small  in  the  Caucasian  race,  much 
larger  in  the  Mongolian,  and  reaches  possibly  its  maximum 
diameter  in  the  American  Indian  and  the  Japanese. 

It  need  not  be  pointed  out  that  like  the  nails  and  epider- 
mis, hairs  are  able  to  be  replaced  only  when  the  reproduc- 
ing Malpighian  layer  at  the  root  of  the  hair  is  left  intact. 

Sebaceous  Glands.  Along  the  tube  of  the  hair  follicle 
in  which  the  shaft  is  immersed  in  the  skin  there  opens  reg- 
ularly a  sebaceous  duct  carrying  a  fatty  secretion  from  the 
sebaceous  gland  into  the  follicle,  there  to  be  poured  upon 
the  shaft  of  the  hair.  This  sebaceous  gland  is  a  flask-like 
outgrowth  from  the  epidermal  cells  of  the  follicle,  and  is 
therefore  epidermal  in  its  origin.  The  function  of  this  se- 
cretion is  not  only  to  preserve  somewhat  the  vitality  of  the 
hair,  but  by  being  poured  upon  the  skin  to  keep  that  in 
pliable  condition  and  to  protect  the  same  from  excessive 
evaporation.  The  secretion  from  these  sebaceous  glands  is 
of  a  fatty  nature.  In  places  where  the  hairs  are  minute 
these  sebaceous  glands  seem  to  open  directly  on  the  surface 
of  the  skin,  an  arrangement  especially  noticeable  on  the 
skin  of  the  face.  The  secretion  of  such  glands  may  fre- 
quently become  thickened  and  so  choke  up  the  glands  in 
question,  a  condition  which  usually  results  in  the  formation 
of  a  pimple,  which  is  nothing  more  than  an  attempt  of  na- 
ture to  empty  the  gland  by  a  process  of  suppuration.  Some- 
times the  mouth  of  the  gland  becomes  filled  with  particles 
of  dust  or  dirt  pressed  down  into  them,  and  so  gives  rise 
to  the  familiar  blackhead.  These  glands  seem  to  be  emp- 
tied as  a  rule  by  the  contraction  of  muscles  which  are  found 
attached  to  each  hair  follicle.  These  muscles  are  bands  of 
plain  muscular  tissue  attached  at  one  end  to  the  under  sur- 
face of  the  corium,  at  the  other  to  the  lower  portions  of  the 


KIDNEYS,    SKIN,    AND    GENERAI,   EXCRETION.  405 

hair  follicle.  By  their  contraction  it  is  probable  that  a  lit- 
tle of  this  sebaceous  secretion  is  squeezed  out  of  the  gland 
into  the  follicle.  These  muscles  are  specially  apt  to  con- 
tract under  certain  conditions  such  as  exposure  to  the  cold, 
and  by  this  contraction  the  follicle  is  pulled  upward  and 
projects  slightly  beyond  the  rest  of  the  epidermis,  producing 
the  little  elevations  described  under  the  somewhat  senseless 
term  of  goose-skin. 

These  glands  as  well  as  hairs  are  absent  from  certain 
portions  of  the  skin  such  as  the  palms  of  the  hands  and  the 
soles  of  the  feet.  A  very  specialized  form  of  such  a  sebaceous 
gland  is  found  among  the  tail  feathers  of  certain  birds  and  is 
called  the  uro-pygeal  gland.  The  secretion  here  is  so 
abundant  that  the  bird  in  question  may  by  means  of  its  bill 
take  the  secretion  for  the  oiling  of  its  entire  coat  of  feath- 
ers. A  special  form  of  these  glands  in  the  human  body  is 
found  along  the  upper  and  lower  eyelids.  These  glands  are 
known  as  the  Meibomian  glands.  The  function  of  the  se- 
cretion at  this  point  is  to  keep  the  edge  of  the  lids  some- 
what oily  and  so  prevent  the  tears  from  running  out  of  the 
eye  over  these  eyelids.  This  is  accomplished  by  taking 
advantage  of  the  familiar  fact  that  water  does  not  very 
readily  run  across  an  oiled  surface.  In  the  ear  there  are 
found  certain  sebaceous  glands  secreting  a  thick,  fatty  sub- 
stance familiar  as  the  ear-wax.  These  glands,  however, 
are  anatomically  not  true  sebaceous  glands  at  all,  in  spite 
of  the  nature  of  their  secretion,  but  belong  to  the  tubular 
sweat  glands.  It  is  in  fact  just  possible  that  these  are  not 
modified  sebaceous  glands  at  all,  but  are  really  sweat  glands 
which  have  taken  on  a  different  function. 

THE  SWEAT  GLANDS. 

Distributed  all  over  the  body,  except  on  the  palms  of 
the  hands  and  on  the  soles  of  the  feet,  are  long  tubular 
glands  known  as  the  sweat  or  sudoriferous  glands.  These 
are  simple  tubular  glands,  the  lower  portion  of  the  tube, 
however,  being  rolled  up  into  a  coil.  This  coil  lies  in  the 


406  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

deeper  portions  of  the  corium,  or  more  generally  in  the  sub- 
cutaneous tissue.  From  this  coil  a  tubular  duct  runs 
through  the  corium  and  epidermis,  carrying  its  secretions 
to  the  surface  of  the  skin.  Instead  of  running  directly  up- 
wards the  duct  winds  through  the  corium  and  epidermis  in 
a  spiral  cork-screw  fashion.  A  cross-section  of  the  tube  of 
this  gland  shows  it  to  be  composed  of  an  investment  of  con- 
nective tissue  and  an  inner  layer  of  columnar  cells  enclosing 
the  lumen.  The  coiled  portion  of  the  tube  in  the  sub- 
cutaneous tissue  is  richly  supplied  with  blood-vessels  and 
nerves.  The  reason  for  this  coiling  of  the  tube  is  no  doubt 
explained  in  the  saving  of  space.  The  explanation  of  the 
spiral  winding  of  the  duct  through  the  skin  is  not  apparent. 
These  glands  are  especially  plentiful  on  the  forehead 
and  under  the  arms.  Rough  calculations  have  placed  the 
number  of  sweat  glands  on  the  entire  body  at  about  2,000,- 
000. 

1. — Nerves.  That  these  glands  are  under  the  control  of 
the  nervous  system  is  beyond  question.  It  is  an  every-day 
observation  that  states  of  emotion,  fright  or  pain  directly 
affect  the  perspiration  of  the  body  and  thus  clearly  point 
to  the  existence  of  sweat  centers  in  the  spinal  cord  and 
brain.  But  evidence  still  more  direct  is  at  hand.  It  is 
possible  to  amputate  a  limb  of  a  cat,  for  instance,  and  by 
stimulating  the  sciatic  nerve,  along  which  the  sweat  fibers 
run,  to  produce  droplets  of  sweat  on  the  balls  of  the  feet, 
and  this  even  when  there  is  no  increase  in  the  blood  supply ; 
in  fact,  when  the  circulation  has  entirely  stopped.  This  is 
conclusive  proof  that  the  process  of  sweating  is  not  a  sim- 
ple filtration  of  water  and  salt  from  the  lymph  or  blood  in 
and  through  these  glands,  but  that  it  is  a  physiological 
phenomenon  under  direct  nervous  control,  and  to  a  large 
extent  independent  of  vascular  conditions. 

Experiments  seem  to  point  to  the  existence  of  lower 
sweat  centers  in  the  spinal  cord  which  may,  however,  under 
special  conditions  be  controlled  by  higher  centers  in  the 


KIDNEYS,    SKIN,    AND    GENERAL   EXCRETION.  407 

brain  itself.  The  existence  of  such  higher  sweat  centers  of 
the  brain  was  just  pointed  out  in  the  familiar  experience  of 
everybody  that  strong  emotions,  especially  great  anxiety,  at 
once  shows  itself  in  an  increased  activity  of  these  glands. 
There  are  certain  drugs  which  have  a  very  specific  effect 
on  these  glands.  Thus,  pilocarpine  will  stimulate  the 
glands  to  active  secretion,  while,  on  the  other  hand,  the 
administration  of  atropine  more  or  less  completely  checks  it. 

2. — Composition  of  the  Sweat.  The  secretion  of  these 
glands,  or  the  sweat  as  it  is  called,  has  a  composition  not 
yet  well  determined.  It  is  difficult  to  get  the  fluid  free 
from  a  sebaceous  admixture.  It  seems  to  consist,  however, 
of  water,  common  salt  and  traces  of  a  number  of  alkaline 
salts.  The  most  important  organic  constituent  of  sweat  is 
the  urea.  This  becomes  especially  plentiful  when  for  some 
reason  the  function  of  the  kidneys  has  been  impaired.  But 
even  when  these  are  normally  discharging  their  duty  there 
is  a  larger  proportion  of  urea  in  the  sweat  than  could  be 
accounted  for  by  simple  filtration,  pointing  to  the  fact  that 
the  cells  which  make  up  the  tube  of  the  sweat  glands  in  an 
active  physiological  way  pick  up  the  urea  from  the  blood 
and  eliminate  it  from  the  body  in  the  perspiration.  In  ad- 
dition to  this  urea  fine  chemical  analyses  have  shown  the 
presence  in  minute  quantities  of  some  of  the  other  sub- 
stances found  in  the  secretion  of  the  kidneys.  For  such 
reason  the  skin  has  been  called  an  excretory  tissue  in  ad- 
dition to  a  protective  one  and  classed  physiologically  with 
the  kidneys  and  lungs.  It  was  formerly  believed  that  the 
death  which  soon  followed  the  varnishing  of  the  skin  of  an 
animal,  a  procedure  which  stopped  up  all  the 'pores  of 
the  skin,  was  due  to  the  fact  that  this  excretory  function  of 
the  skin  had  been  stopped.  Such  an  explanation  is,  how- 
ever, wrong,  later  experiments  proving  that  the  death  of 
such  a  varnished  animal  results  from  the  increased  loss  of 
heat  which  the  varnished  surface  of  the  body  radiates 
away. 


408  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

It  was  in  the  chapter  on  heat  pointed  out  in  what  an 
important  and  integral  way  the  perspiration  figured  in  main- 
taining a  constant  and  unvarying  temperature  of  the  body. 

3. — Origin  of  Sweat  Glands.  In  their  origin  sweat 
glands,  too,  are  epidermal.  They  arise  in  early  embryonic 
life  as  outgrowths  of  the  epidermis,  these  down-growths  soon 
becoming  hollow  and  with  secondary  changes  transforming 
themselves  into  the  adult  structure  of  the  gland. 


CHAPTER  XIX. 


THE  GENERAL  ANATOMY  AND  PHYSIOLOGY  OF 
THE  NERVOUS  SYSTEM. 

In  the  discussion  of  the  various  systems  of  the  body  so 
far,  they  have  been  treated  as  acting  more  or  less  inde- 
pendently of  each  other.  We  have  now  left  to  consider 
that  large  system  whose  function  it  is  to  co-ordinate  these 
various  systems  into  a  harmoniously  working  whole.  This 
statement  of  the  function  of  the  nervous  system  covers  at 
one  sweep  its  entire  physiology,  notwithstanding  the  mul- 
titude of  ways  in  which  this  is  accomplished.  Possibly  the 
most  fundamental  point  in  discussing  this  system  is  its  one- 
ness or  unity.  Sometimes  for  arbitrary  reasons  or  for  mere 
convenience  sake  we  speak  of  several  nervous  systems. 
This  is  physiologically  wrong.  The  entire  system  of  nerves, 
ganglia  and  higher  centers  are  all  bound  together  and  phy- 
siologically are  a  unit.  This  is  true  even  in  spite  of  the 
fact  that  certain  parts  of  this  system  have  more  or  less 
specialized  functions,  for  even  in  this  case  the  co-ordina- 
tion and  the  successive  subordination  is  finally  so  perfect 
that  unifying  results  only  are  reached.  It  seems  desirable, 
however,  in  order  to  facilitate  the  discussion  of  these 
nervous  tissues  to  adopt  the  usual  classification  into — 

First,  the  cerebro-spinal  system,  including  the  brain 
and  the  cranial  nerves,  and  the  spinal  cord  and  the  spinal 
nerves. 

Second,  the  sympathetic  system,  including  two  chains 
of  ganglia  lying  along  the  back-bone  and  extending  from 
the  upper  cervical  through  the  lumbar  region,  and  the 
nerves  which  emanate  from  these  ganglia. 

Third,  the  sporadic  system,  not  a  connected  system  at 
all,  but  consisting  of  various  ganglia  scattered  throughout 

(409) 


410  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  body  not  included  in  the  two  other  systems.  Such 
ganglia  are  those  of  the  heart,  the  plexuses  of  Auerbach 
and  Meissner  in  the  intestine,  the  intrinsic  ganglia  of 
blood-vessels,  the  solar  plexus  of  the  mesentery,  etc.  A 
sharp  distinction  between  these  three  systems  cannot  at  all 
be  drawn.  The  spinal  nerves  are  connected  with  the  sym- 
pathetic nerves,  and  both  these  nerves  may  run  into  spora- 
dic ganglia. 

NERVOUS  ELEMENTS. 

In  studying  in  detail  any  of  these  systems  two  kinds  of 
nervous  structures  are  at  once  discernible: 

1. — Nerves,  Nerve  Trunks  and  Plexuses.  By  dissect- 
ing a  body  one  meets  almost  everywhere  whitish  looking 
threads  which  are  nerves.  These  might  easily  be  mistaken 
for  tendon  threads  or  other  connective  tissue  fibers.  If  by 
means  of  the  scalpel  the  course  of  such  a  thread  or  cord  is 
followed  it  is  soon  seen  to  divide  and  sub-divide  until  the 
finer  ramifications  are  lost  among  the  muscles  or  glands  or 
in  the  skin.  If  the  microscope  should  be  called  to  aid  it 
would  be  possible  to  actually  see  these  nerve  terminations 
in  many  instances,  such  as  their  endings  in  the  nerve- 
plates  of  the  voluntary  muscles  or  in  the  tactile  corpuscles 
of  the  skin.  If,  on  the  other  hand,  one  should  follow  the 
course  of  such  a  nerve  inward,  it  would  be  seen  to  unite 
with  other  nerves,  until  finally  the  nerve  would  be  found 
entering  the  spinal  cord  or  brain,  or  at  least  some  central 
ganglion.  Such  whitish  cords  are  called  nerve  trunks.  A 
cross-section  of  such  a  nerve  trunk  would  show  that  it  is 
composed  of  very  many  smaller  cords,  the  nerve  fibers,  and 
that  the  trunk  is  really  nothing  more  than  a  collection  of 
fibers  running  in  the  same  direction  wrapped  in  a  common 
envelope  of  white  connective  tissue.  It  is  this  white  con- 
nective tissue  envelope  and  not  the  nerve  substance  itself 
which  gives  to  the  nerve  trunk  the  color  in  question.  Not 
infrequently  by  following  a  nerve  trunk  it  might  be  seen  to 
send  off  communicating  branches  to  other  nerve  trunks,  and 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         411 

these  in  turn  to  still  others,  and  so  there  would  be  produced 
networks  of  fibers.  These  networks  are  called  plexuses. 
It  is  by  means  of  these  plexuses  that  an  individual  nerve 
fibril  of  one  trunk  may  find  its  way  into  other  trunks  and  so 
reach  removed  parts  of  the  body.  This  makes  it  possible 
for  a  nerve  trunk  to  contain  near  its  end  fibers  which  it  did 
not  have  at  its  beginning,  but  which  reached  it  along  its 
course.  While  such  plexuses  are  very  generally  distributed 
all  over  the  body  there  are  peculiarly  large  ones  in  the 
shoulder  and  lumbar  regions,  forming  respectively  the  spinal 
nerve  plexuses  that  go  to  the  arms  and  limbs. 

2. — Nerve  Centers  or  Ganglia.  When  the  course  of  a 
nerve  is  followed  inward  it  is  soon  found  to  end  either  in  the 
brain,  spinal  cord,  sympathetic  system,  or  in  isolated  gan- 
glia over  the  body.  All  these  structures  named  are  nerve 
centers;  that  is,  they  are  nervous  centers  from  which  nerve 
fibers  arise.  These  nerve  centers  may  be  large,  as  many  of 
those  in  the  brain,  or  they  may  be  small  aggregations  of 
nervous  tissue  like  the  individual  centers  of  the  sympa- 
thetic system.  Centers  lying  more  or  less  separate  and 
having  a  distinct  outline  are  called  ganglia. 

A  ganglion  is  in  essence  nothing  more  than  a  group  of 
nerve  cells  with  which  the  nerve  fibers  entering  the  gan- 
glion are  physiologically  connected.  These  groups  of  nerve 
cells  are  of  course  usually  surrounded  with  a  more  or  less 
complete  coat  of  connective  tissue  intended  for  protection. 
While  anatomically  this  description  suits  all  ganglia,  phy- 
siologically there  are  distinct  kinds. 

From  this  it  will  be  seen  that  the  entire  nervous  system 
is  composed  of  nerve  cells  more  or  less  grouped  into  dis- 
tinct ganglia  and  of  nerve  fibers  which  run  out  from  these 
ganglia  connecting  them  with  each  other,  or  connecting  the 
ganglia  with  distant  glands,  muscles,  skin,  etc.  A  detailed 
histological  description  of  these  nerve  fibers  and  their 
coats,  and  of  the  nerve  ganglia  and  their  aggregation  in 
turn  into  larger  centers  is  reserved  for  the  chapter  on  the 


412  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

finer  architecture  of  the  nervous  system,  it  being  the  inten- 
tion in  these  preliminary  paragraphs  to  deal  simply  with 
those  points  of  the  nervous  system  included  under  its  gross 
anatomy. 

THE  BRAIN  AND  SPINAL  CORD. 

By  far  the  most  important  system,  both  with  reference 
to  its  special  psychical  functions  and  its  general  control 
over  the  other  systems,  is  the  cerebro-spinal  system.  This 
consists  of  the  brain  and  spinal  cord,  and  the  nerves  issu- 
ing from  them.  The  brain  and  spinal  cord  are  continuous 
through  the  foramen  magnum,  a  large  opening  in  the  occip- 
ital bone. 

The  Membranes  of  the  Cerebro- Spinal  System. 

In  the  examination  of  these  systems  one  is  peculiarly 
impressed  with  the  efficient  way  in  which  they  are  enclosed 
within  bony  and  membranous  coverings.  The  brain  is  en- 
cased in  the  bony  cranium,  while  the  spinal  cord  is  almost 
equally  protected  in  the  neural  arches  formed  by  the  verte- 
brae. In  addition  to  this  bony  envelope  both  brain  and 
spinal  cord  are  covered  with  three  membranes.  Lying 
next  to  the  nervous  tissue  is  a  delicate  thin  membrane 
called  the  pia-mater.  This  dips  down  into  all  the  convo- 
lutions and  configurations  of  brain  and  spinal  cord,  and 
serves  especially  to  carry  the  blood-vessels  nourishing  them. 
Ikying  next  to  the  bone  is  an  exceedingly  tough  dense  mem- 
brane formed  almost  wholly  of  white  closely  woven  con- 
nective fibers  called  the  dura-mater.  Between  the  dura- 
mater  and  the  pia-mater  there  is  a  spongy  membrane  called, 
on  account  of  its  web-like  nature,  the  arachnoid  membrane. 
The  dura-mater  figures  not  only  as  an  enveloping  membrane 
of  the  brain  and  spinal  cord,  but  serves  as  a  periosteum  for 
the  cranial  bones  as  well.  While  these  membranes  sur- 
round the  brain  very  closely  the  dura-mater  does  not  invest 
the  spinal  cord  in  the  same  way,  but  here  frequently  leaves 
quite  a  space  between  the  pia-mater  and  itself,  in  this  way 
covering  even  the  spinal  root  ganglia  lying  along  the  spinal 


ANATOMY.   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         413 

cord.     In  fact,  the  dura-mater  is  loosely  attached  around 
the  spinal  cord  and  does  not  serve  as  a  periosteum  for  the 


Fig.  136.— SECTION  OF  THE  SPINAL  CORD  SHOWING  TKE  ARRANGEMENT  OF  ITS  INVEST- 
ING MEMBRANES.     (After  Key  and  Retzius.) 

a,  dura  mater;  b,  arachnoid;  c,  posterior  septum;  d,  e,f,  subarachnoid  tissue;  A,  an- 
terior root  fibers  cut;     A,  I,  subarachnoid  space.          ^     ^     ' 

vertebrae,  these  bones  having  a  periosteum  of  their  own. 
In  the  meshes  of  the  arachnoid  membrane  there  is  usually 
contained  a  small  quantity  of  lymph-like  liquid  called  the 
cerebro-spinal  liquid.  It  is  not  probable  that  this  has  any 
specific  function. 

The  Spinal  Cord. 

The  spinal  cord  is  a  cylinder  of  nervous  matter  enclosed 
in  the  neural  arches.  Its  average  length  is  about  seven- 
teen inches.  It  does  not,  therefore,  reach  from  the  cer- 
vical region  entirely  through  the  lumbar.  In  fact,  the 
neural  space  in  the  lower  lumbar  region  is  occupied  by  a 
number  of  nerve  fibers  from  the  spinal  cord,  while  the  cord 
itself  is  here  reduced  to  a  slender  filament  called  the  filum 
terminate  which  runs  to  the  end  of  the  neural  canal  in  the 
sacrum. 

The  cord  is  not  quite  round  in  cross-section,  it  being  a 
little  wider  from  side  to  side  than  from  before  backwards. 
Its  average  diameter  is  about  three-fourths  of  an  inch.  It 


414 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


shows,  however,  two  enlargements  along  its  course,  one  in 
the  cervical  region  called  the  cervical  enlargement,  and  a 
second  at  the  beginning  of  the  lumbar  region  called  the 
lumbar  enlargement.  It  weighs  from  one  and  one-half  to 
two  ounces. 

The  spinal  cord  gradually  shades  off  into  the  brain,  and 
the  point  at  which  one  is  said  to  cease  and  the  other  to  be- 
gin is  quite  arbitrary.  There  is  no 
sudden  transition  from  one  to  the  other. 
If  a  cross-section  be  made,  the  cord  is 
seen  to  consist  of  two  halves,  this  bi- 
lateral arrangement  being  caused  by 
two  deep  grooves  or  fissures  running 
longitudinally  along  the  cord  and  al- 
most separating  it  into  a  right  and  left 
lobe.  The  division,  however,  is  not 
complete,  the  anterior  and  the  posterior 
fissures  not  meeting,  but  the  two  hemi- 
spheres being  connected  near  the  mid- 
dle by  a  commissure  consisting  partly 
of  gray  matter,  and  anterior  to  this  of 
white  matter.  The  posterior  fissure 
reaches  down  to  the  gray  matter,  and 
the  anterior  fissure  to  the  white  com- 
missure just  referred  to.  In  the  center 
of  the  gray  commissure  is  the  cross- 
section  of  a  canal  running  lengthwise 
through  the  spinal  cord  and  connected 
in  the  brain  with  the  ventricles.  This 
is  called  the  central  canal,  or  canal  is 
centralis.  It  probably  has  no  specific 
physiological  function,  but  its  presence  is  easily  explained 
by  reference  to  the  embryonic  development  of  the  spinal 
cord  and  brain. 

A  cross-section  of  the  cord  does  not  show  a  uniform  ap- 
pearance, but  shows  a  grouping  into  two  tissues,  so  dis- 
posed that  the  central  gray  substance  is  arranged  somewhat 


Fig.  137.— CROSS-SECTION  OF 

HUMAN        SPINAL        CORD, 
TWICB   NATURAL   SIZE. 

A,  cervical  region;  B,  dor- 
sal region ;  C,  lumbar  region ; 
a,  anterior  root;  p,  posterior 
root. 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         415 

in  the  form  of  a  capital  "H."  The  commissure  of  this  H 
is  the  gray  commissure  just  mentioned,  which  contains  the 
central  canal.  Each  limb  of  the  H  shows,  however,  a 
shorter  and  thicker  anterior  branch  and  a  somewhat  more 
slender  posterior  branch.  These  are  called  respectively  the 
anterior  and  posterior  horns  or  cornua.  The  remaining 
portion  of  the  cord  outside  of  this  central  H  is  composed  of 
white  matter  which  examination  with  the  microscope  re- 
veals to  be  cross-sections  of  nerve  fibers  which  are  here 
passing  along  the  cord.  The  central  gray-shaped  H  owes 
its  grayish  color  to  the  fact  that  it  contains  aggregations  of 
nerve  cells,  which  are  always  gray,  and  of  nerve  fibers 
which  do  not  possess  the  white  medullary  coat,  and  so  are 
also  gray.  On  the  other  hand,  the  white  appearance  of  the 
surrounding  portions  is  due  to  the  presence  of  the  white 
medullary  coats  of  the  nerve  fibers.  Just  anterior  to  the 
gray  commissure  is  the  white  commissure  already  men- 
tioned, formed  by  fibers  connecting  the  white  matter  of  one 
side  with  the  white  of  the  other.  By  means  of  the  horns 
of  the  gray  matter  the  area  of  the  cord  is  divided  into 
several  easily  distinguishable  regions.  The  white  matter 
included  between  the  anterior  horns  is  spoken  of  as  the 
anterior  white  column,  that  included  between  the  posterior 
horns  is  called  the  posterior  white  column,  while  that  por- 
tion on  each  side  lying  in  the  hollow  of  each  of  the  cres- 
cent-shaped limbs  is  called  the  lateral  column.  These 
columns  are  of  the  deepest  interest  in  the  discussion  of  the 
course  of  fibers  through  the  brain  and  cord,  a  point  to  be 
treated  further  on 

The  Spinal  Nerves. 

If  a  cross-section  of  the  cord  had  been  made  between  the 
origins  of  the  spinal  nerves,  the  section  as  just  described 
would  have  included  all  the  points  visible.  If,  however,  the 
section  should  have  passed  through  that  region  of  the  cord 
from  which  a  pair  of  spinal  roots  takes  its  issue  several  ad- 
ditional points  would  appear.  Running  out  from  the  an- 
terior and  posterior  horns,  fibers  might  be  traced  leaving 


416  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  cord,  running  for  some  distance  laterally  from  the  cord 
as  separate  trunks,  but  before  leaving  the  dura-mater,  unit- 
ing on  each  side  to  form  a  single  spinal  nerve.  On  the 
posterior  root  of  the  spinal  nerve  just  previous  to  its  union 
with  the  anterior  root,  occurs  a  ganglion  called  for  evident 
reasons  the  posterior  spinal  root  ganglion.  The  physiolog- 
ical significance  of  these  roots  need  not  concern  us  here, 
save  the  preliminary  statement  that  the  fibers  which  leave 
the  cord  from  the  anterior  horn  are  motor  in  their  nature ; 
that  is,  carry  impulses  outward  towards  the  muscles,  while 
the  fibers  entering  at  the  posterior  horn  are  sensory  fibers 
carrying  sensations  inward  to  the  cord  and  brain. 

Immediately  after  the  formation  of  the  spinal  nerve  by 
the  union  of  sensory  and  motor  trunks  it  divides  into  three 
branches,  a  posterior  primary,  distributed  mainly  to  the 
skin  and  muscles  of  the  back,  an  anterior  primary,  giving 
off  nerves  for  the  sides  and  ventral  portion  of  the  trunk 
and  for  the  limbs,  and  a  third  communicating  branch  which 
runs  to  the  neighboring  sympathetic  ganglion.  It  is  through 
this  connecting  branch  that  the  co-ordination  and  subordi- 
nation of  the  sympathetic  system  is  effected. 

Thirty-one  pairs  of  such  spinal  nerve  trunks  arise  from 
the  spinal  cord,  leaving  the  neural  canal  through  the  inter- 
vertebral  foramina.  Each  of  these  spinal  nerves  has  a 
specific  name,  the  name  being  derived  from  the  vertebra 
situated  immediately  in  front  of  it.  Thus,  the  nerve  that 
arises  between  the  second  and  third  thoracic  vertebrae  is  the 
second  thoracic  spinal  nerve ;  that  which  arises  between  the 
fourth  and  fifth  lumbar  vertebrae  is  the  fourth  lumbar  nerve. 
The  spinal  nerves  which  arise  in  the  lower  lumbar,  sacral 
and  coccygeal  region  run  down  through  the  neural  canal, 
occupying  the  space  in  this  portion  which  the  cord  has 
further  up,  the  cord  being  here  reduced  to  the  filum  ter- 
minale.  This  big  bunch  of  nerves  is  called  the  horse's 
tail,  or  cauda  eq^l^na. 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.          417 
GENERAL  DISTRIBUTION  OF  THE  SPINAL  NERVES. 

It  would  be  quite  undesirable  from  the  standpoint  of  an 
elementary  text-book  to  give  with  surgical  exactness  the 
distribution  of  these  thirty-one  pairs  of  spinal  nerves. 
Suffice  the  general  statement  that  these  spinal  nerves  sup- 
ply the  voluntary  muscles  of  the  neck  and  the  trunk ;  that 
as  the  phrenic  nerve  they  control  the  diaphragm;  as  sen- 
sory nerves  they  are  distributed  to  the  entire  skin  of  neck, 
trunk  and  limbs,  while  as  motor  nerves  they  innervate  the 
muscles  of  the  limbs  and  figure  in  all  their  voluntary  move- 
ments. In  a  word,  it  may  be  said  that  the  spinal  nerves 
innervate  all  that  portion  of  the  body  below  the  head  from 
which  we  derive  special  sensations  or  in  which  we  are  able 
to  produce  voluntary  movements.  In  addition  to  this,  com- 
municating branches  reach  the  sympathetic  system  and 
bring  it  into  physiological  connection  with  the  brain  and 
spinal  cord. 

THE  BRAIN. 

Under  the  term  "brain"  is  included  all  that  portion  of 
the  cerebro-spinal  system  lying  above  and  including  the 
medulla  oblongata.  It  consists  of  three  main  divisions  ap- 
parent at  once  to  the  unaided  eye:  the  large  fore-brain  or 
cerebrum,  the  hind-brain  consisting  of  the  cerebellum  and 
the  medulla  oblongata  lying  immediately  below  it,  and  the 
mid-brain  lying  between  the  cerebrum  and  hind-brain  and 
consisting  of  the  corpora  quadrigemina  and  crura  cerebri. 

Weight.  The  weight  of  the  brain  varies  considerably, 
an  average  weight  being  in  the  neighborhood  of  fifty 
ounces  in  the  adult  male  and  about  forty-five  in  the  female. 
Of  this  weight  of  fifty  ounces  the  fore-brain  or  cerebrum 
weighs  about  forty-four,  being  therefore  very  much  larger 
than  the  hind-brain  and  mid-brain  together.  In  fact,  it 
laps  entirely  over  the  other  portions,  so  that  a  view  from 
above  would  not  disclose  either  the  cerebellum  or  mid- 
brain.  This  especial  development  of  the  fore-brain  is,  how- 
ever, a  characteristic  of  the  human  species  alone.  As  we 


418  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

go  down  the  animal  scale  the  relative  difference  decreases 
until  in  some  of  the  lower  vertebrates  the  fore-brain  is  the 
smallest  of  the  divisions.  This  is  especially  true  in  the 
fishes,  in  which  the  mid-brain  or  optic  lobes  form  the  bulk 
of  this  organ.  The  cerebellum  and  medulla,  on  the  other 
hand,  do  not  decrease  in  the  same  proportion,  but  are  rela- 
tively large  in  all  animals.  The  disproportionate  size  of  the 
human  cerebrum  makes  possible  those  higher  psychical 
functions  which  belong  to  man  alone. 

Convolutions.  The  cerebrum  is  divided  by  a  deep 
median  fissure  into  two  almost  separate  halves  called  the 
cerebral  hemispheres.  Viewed  from  the  top  and  sides  the 
surface  of  the  cerebrum  is  thrown  into  deep  convolutions  or 
gyri.  While  these  convolutions  occur  in  the  brains  of  many 
of  the  lower  animals  they  are  much  deeper  in  the  human 
species,  and  there  is  even  an  increase  in  the  depth  as  we 
proceed  from  the  lower  to  the  higher  races  of  mankind. 
These  convolutions  find  their  explanation  in  the  fact  that 
the  surface  of  the  brain  is  thereby  materially  increased. 
Rough  calculations  on  the  actual  surface  of  the  average 
brain  show  that  it  may  reach  an  extent  almost  equal  to 
that  of  the  larger  portion  of  the  trunk  itself,  but  by  means 
of  these  foldings  this  surface  is  enclosed  in  the  relatively 
small  cranium.  The  desirability  for  a  large  cortical  surface 
is  apparent  when  it  is  remembered  that  the  principal  cells 
concerned  in  sensation  and  volition  are  found  here.  While 
these  convolutions  seem  to  run  without  any  appearance  at 
regularity,  and  while  in  detail  they  do  differ  somewhat  in 
different  individuals,  their  general  plan  is  constant,  and  by 
means  of  them  spots  on  the  cortex  of  the  brain  are  local- 
ized. A  few  of  the  principal  convolutions  only,  need  be 
mentioned  here.  One  of  these  is  the  large  fissure  of  Syl- 
vius, on  each  side  of  the  brain  which  lies  between  the  lateral 
lobes  of  the  brain  and  the  main  portion,  running  from  the 
base  of  the  brain  upwards  and  backwards  towards  the  oc- 
cipital region.  Connecting  with  the  fissure  and  running 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         419 

upwards  towards  the  top  of  the  brain  separating  from  the 
main  portion  of  the  cerebrum,  the  frontal  lobes,  is  the 
fissure  of  Rolando.  The  fissure  of  Sylvius  is  important  as 
being  the  most  apparent  and  deepest  furrow.  The  fissure 
of  Rolando  is  interesting  as  being  the  region  along  which 
many  of  the  centers  of  conscious  volition  have  been  by  ex- 
periments localized.  If  the  fissure  of  Sylvius  be  opened 
with  the  fingers  it  discloses  to  view  a  lobe  of  the  brain 
hidden  in  this  fissure  known  as  the  Island  of  Rcil.  If  from 
the  top  the  two  cerebral  hemispheres  be  pushed  apart  it  will 
be  seen  that  the  median  fissure  reaches  down  to  a  white 
band  of  connecting  fibers  which  runs  from  one  hemisphere 
to  the  other.  This  band  of  connecting  fibers  is  called  the 
corpus  callosum. 

Base  of  Drain.  If  now  the  base  of  the  cerebrum  be 
studied  it  reveals  a  number  of  structures  easily  recognizable 
with  the  unaided  eye.  Lying  immediately  under  the  frontal 
lobes  are  the  olfactory  lobes.  These  are  bits  of  grayish, 
nervous  tissue  and  are  the  nerves  concerned  in  the  sense  of 
smell.  They  are  quite  inconspicuous  in  man,  but  in  some 
of  the  lower  animals  reach  very  large  proportions,  some- 
times being  larger  than  the  cerebral  hemispheres  themselves. 
This  may  probably  be  interpreted  as  meaning  that  the  sense 
of  smell  is  relatively  dull  in  man  as  compared  with  many  of 
the  lower  forms,  which  have  to  rely  upon  this  sense  in 
searching  for  their  food  or  avoiding  their  enemies. 

Immediately  back  of  the  olfactory  lobes  the  large  optic 
nerves  arise.  These  optic  nerves  seem  to  cross  at  the  base 
of  the  brain  in  the  optic  commissure  and  are  continued  back 
into  the  brain  beyond  this  commissure  as  the  optic  tracts. 
These  tracts  may  be  followed  some  distance  around  the 
crura  cerebri  into  the  tissue  of  the  brain.  There  is  not  a 
complete  crossing,  however,  of  the  optic  nerves  at  the  com- 
missure, but  the  decussation  is  limited  to  half  of  the  fibers 
so  that  the  optic  nerve  on  each  side  consists  of  half  of  the 
fibers  from  its  own  optic  tract,  the  other  half  from  the  op- 
posite optic  tract  which  reached  it  in  the  commissure. 


420  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

Immediately  behind  the  optic  commissure  there  is  a  fun- 
nel-like projection  called  the  infundibulum.  At  the  end  of 
this  infundibulum  lies  a  peculiar  gland-shaped  body  familiar 
as  the  pituitary  body,  a  structure  described  in  the  chapter 
on  the  ductless  glands.  The  infundibulum  is  hollow,  the 
cavity  in  the  same  being  an  extension  of  the  third  ventricle. 
On  account  of  the  thinness  of  its  walls  and  the  difficulty 
with  which  the  pituitary  body  is  removed  from  the  skull, 
these  structures  are  usually  torn  off  in  prepared  brains  and 
the  place  of  the  infundibulum  is  indicated  only  by  an  open- 
ing leading  into  the  third  ventricle. 

Posterior  to  the  infundibulum  and  just  in  the  angle  of 
the  crura  cerebri  lie  two  small  whitish  elevations  each  about 
the  size  of  a  small  bullet,  the  corpora  albicantia.  It  will  be 
pointed  out  further  on  that  these  corpora  albicantia  are  pro- 
jections caused  by  the  sudden  bending  back  at  this  point  of 
the  fornices,  which  are  bands  of  nerve  fibers  running 
through  the  brain.  These  fibers  run  to  the  bottom  of  the 
brain  as  if  to  leave  it  at  this  point,  and  then  make  a  sharp 
turn  and  run  almost  directly  backwards.  It  is  this  lobe  of 
the  fornix  which  projects  from  the  brain  below,  and  which, 
consisting  of  white  nerve  fibers,  gives  to  these  structures 
their  peculiar  appearance. 

Following  this  it  may  be  noticed  that  the  continuation 
of  the  cord  here  divides  into  two  forks,  one  running  to  the 
right  hemisphere  and  the  other  to  the  left.  These  two  forks 
are  called  the  legs  of  the  brain,  or  the  crura  cerebri.  They 
are,  of  course,  the  big  tracts  by  means  of  which  the  hemis- 
pheres of  the  brain  are  put  in  direct  communication  with  the 
nervous  system  below. 

Near  the  middle  of  the  crura  cerebri  arises  the  third  pair 
of  cranial  nerves,  the  stumps  of  which  usually  appear  as  rel- 
atively large  nerves. 

A  little  distance  farther  back  lies  the  pons  Varolii, 
readily  distinguishable  as  a  thickened  band  around  the  me- 
dulla. This  pons  or  bridge  consists  largely  of  fibers  which 
run  across  the  cord  at  this  point  and  connect  the  two  sides 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         421 

of  the  cerebellum.  In  a  general  way,  disregarding  certain 
sets  of  fibers  the  cerebellum  and  the  pons  may  be  compared 
to  a  signet  ring,  the  band  of  which  is  the  pons,  the  signet 
being  the  large  cerebellum  itself,  the  finger  the  cord  pass- 
ing between.  It  is  well  to  repeat  again  that  this  analogy  is 
not  quite  true  either  anatomically  or  physiologically,  but  the 
detailed  course  of  the  fibers  at  this  point  will  be  followed  in 
a  succeeding  chapter. 

Immediately  back  of  the  pons  is  the  medulla,  with  its 
widest  portion  near  the  pons  and  gradually  tapering  back- 
ward until  it  reaches  the  size  of  the  cord  into  which  it 
gradually  blends.  Along  the  pons  and  the  medulla  arise  the 
remaining  cranial  nerves. 

While  all  of  these  structures  at  the  base  of  the  brain 
have  been  described  in  connection  with  the  cerebrum,  some 
belong  to  the  mid  or  hind-brain  in  reality.  The  fore-brain 
extends  to  the  beginning  of  the  crura  cerebri  and  the 
mid-brain  as  seen  from  below  includes  the  crura  cerebri, 
while  the  hind-brain  consists  of  the  pons,  medulla  oblon- 
gata  and  cerebellum.  If  by  means  of  the  fingers  the  cere- 
brum and  cerebellum  be  pushed  apart  by  tearing  away  the 
brain  coverings  which  hold  them  in  place,  here,  the  dorsal 
view  of  the  mid-brain  appears.  This  is  marked  by  four 
hemispherical  eminences  called  the  corpora  quadrigemina. 
Of  these  the  anterior  pair  is  much  larger  and  is  called  the 
nates,  the  posterior  pair  the  testcs.  These  corpora  quadri- 
gemina occupy  on  the  dorsal  side  of  the  mid-brain  the  posi- 
tion held  by  the  crura  cerebri  on  the  base.  If  the  cerebrum 
and  the  mid-brain  be  torn  apart  somewhat,  there  will  be 
seen  lying,  just  anterior  to  the  corpora  quadrigemina  and 
on  the  median  line  of  the  body,  a  small  gland-like  structure 
about  the  size  of  a  pea  or  smaller,  known  as  the  pineal 
gland.  This  pineal  gland  is  not  connected  with  the  mid- 
brain  at  all,  but  arises  from  the  two  optic  thalami  lying 
immediately  anterior.  This  structure  was  the  object  of  some 
speculation  formerly  when  the  view  was  advanced  that  being 
the  only  unpaired  structure  in  the  brain  it  must  be  the  seat 


422  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

of  the  soul,  the  soul  being  considered  an  individual  and  not 
divisible  into  halves.  Such  speculation  soon  came  to  grief, 
however,  when  it  was  discovered  that  this  pineal  gland  was 
relatively  larger  in  the  lower  animals,  and  as  greater  dimen- 
sions of  soul  were  not  to  be  attributed  by  these  thinkers  to 
the  brute  creation,  this  view  had  to  be  abandoned.  Its  sci- 
entific explanation  is  now,  however,  evident,  it  being  noth- 
ing more  than  the  stump  of  an  optic  nerve  which  in  the 
early  history  of  evolution  connected  with  a  third  eye.  All 
traces  of  the  eye  are  gone  in  all  the  higher  animals,  but  the 
proximal  stump  of  the  nerve  is  still  present.  In  some  of  the 
lower  animals,  certain  forms  of  lizards,  the  pineal  gland 
still  connects  with  a  retinal  structure,  although  even  here  it 
has  ceased  to  be  functional. 

The  surface  of  the  cerebellum  differs  essentially  from  that 
of  the  cerebrum.  It  has  no  true  convolutions,  although 
marked  by  a  series  of  transverse  ridges.  It  is  divided  into 
three  lobes,  a  central  or  middle  lobe  and  the  two  lateral 
lobes.  At  the  outer  lower  edge  of  each  lateral  lobe  there  is 
a  small  added  lobe  called  the  flocculus. 

The  Interior  of  the  Brain. 

The  Ventricles  of  the  Brain.  Before  describing  the 
structures  lying  within  the  brain  it  seems  desirable  to  show 
the  topography  of  the  ventricles  of  the  brain  in  order  that 
the  other  structures  may  be  located  with  reference  to  these. 

The  central  canal  of  the  spinal  cord  runs  upward  into  the 
medulla  and  here  widens  out  into  a  large  ventricle  called 
the  fourth  ventricle  of  the  brain.  This  ventricle  lies  im- 
mediately below  the  cerebellum.  Instead  of  lying  in  the 
center  of  the  medulla  it  lies  very  close  to  the  dorsal  surface, 
that  is,  next  to  the  cerebellum,  and  separated  from  it  by  a 
very  thin  wall  only.  This  wall  is  easily  torn  and  the  inte- 
rior of  the  ventricle  laid  bare.  The  width  of  the  ventricle 
here  is  considerable,  a  half  inch  or  more.  Proceeding  up- 
wards the  ventricle  again  narrows  into  a  small  canal  in  the 
mid-brain  and  as  such  a  small  canal  passes  entirely  through 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         423 

this  part.  This  small  caiial  is  known  as  the  aqueduct  of 
Sylvius,  or  more  usually  the  iter.  This  iter  lies  between 
the  copora  quadrigemina  and  the  crura  cerebri.  Immediately 
upon  reaching  the  cerebrum  the  iter  enlarges  into  the  third 
ventricle.  This  ventricle  lies  between  the  optic  thalami  and 
extends  down  into  the  infundibulum  already  described.  Both 
the  fourth  ventricle,  the  iter,  and  the  third  ventricle  lie  in  a 
median  position.  At  the  forward  end,  the  third  ventricle 
narrows  into  two  openings,  known  as  the  foramina  of 
Monro,  and  each  of  these  opens  at  once  into  a  large  lateral 
ventricle  which  lies  within  each  cerebral  hemisphere.  These 
lateral  ventricles  are  relatively  very  large,  and  extend  from 
near  the  front  of  the  brain  to  the  occipital  region,  while  a 
horn  of  this  ventricle  dips  down  almost  to  the  bottom  of 
the  lateral  lobes. 

The  two  lateral  ventricles  are  separated  from  each  other 
by  a  thin  partition,  which  partition  in  front  of  the  third 
ventricle  is  called  the  septum  hicidum.  This  septum  luci- 
dum  is  really  double,  enclosing  a  small  space  within  itself. 
This  space  is  called  the  fifth  ventricle  of  the  brain.  It  is 
necessary,  however,  to  bear  in  mind  that  this  fifth  ventricle 
is  not  a  true  ventricle  at  all.  It  has  no  connection  what- 
ever with  the  other  ventricles,  and  is  really  only  an  acci- 
dental opening  formed  in  the  septum  lucidum  as  the  brain 
developed.  . 

Interior  Structures.  If  with  a  scalpel  sections  of  the  cer- 
ebrum parallel  to  the  base  of  the  brain  should  be  cut  off 
there  would  soon  be  reached  the  bottom  of  the  fissure  divid- 
ing the  brain  into  two  hemispheres.  Examination  of  this 
bottom  shows  it  to  be  made  up  of  a  sheet  of  white  nerve 
fibers  extending  from  one  hemisphere  to  the  other.  This 
sheet  of  connecting  fibers  is  the  corpus  callosttm.  If  after 
having  been  laid  open,  the  corpus  callosum  is  gently  cut 
loose  and  lifted  off  the  structures  below  it,  the  two  lateral 
ventricles  come  to  view,  the  corpus  callosum  forming  the 
roof  of  these  lateral  ventricles.  The  two  lateral  ventricles 


424  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

can  then  be  easily  seen  to  be  separated  from  each  other  by 
a  band  of  tissue  running  perpendicularly  along  the  median 
line  of  the  brain  from  the  corpus  callosum  to  the  floor  of 
the  ventricles,  while  towards  the  front  of  the  brain  this 
septum  would  be  continuous  with  the  septum  lucidum. 

If  the  corpus  callosum  should  be  entirely  removed  the 
entire  floor  of  each  ventricle  is  exposed.  In  the  anterior 
portion  of  this  floor  lie  the  corpora  striata,  eminences  of  gray 
nerve  matter  each  about  the  size  of  an  almond.  In  position 
these  corpora  striata  lie  just  to  the  right  and  left  of  the  sep- 
tum lucidum.  The  floor  in  the  posterior  portion  of  the 
ventricles  is  made  by  a  triangular  mass  of  white  tissue  with 
its  broad  side  towards  the  mid-brain  and  tapering  towards 
the  septum  lucidum.  This  white  tissue  bends  abruptly 
downward  posteriorly  at  each  side  and  runs  to  the  base  of 
the  lateral  lobes  of  the  brain  following  the  ventricle  in  this 
region.  This  broadened  portion  is  called  the  hippocampiis . 
Towards  the  septum  lucidum  this  becomes  gradually  nar- 
rower and  where  it  bends  downwards  it  is  on  each  side  called 
\htfornix  (pillar).  Immediately  under  the  fornix  on  each 
side,  and  between  it  and  the  optic  thalamus  beneath  is  the 
foramen  of  Monro  already  referred  to.  The  fornices  are  not 
continuous  with  the  septum  lucidum,  as  they  seem  at  first 
sight  to  be,  but  bend  abruptly  downwards  in  front  of  the 
third  ventricle  reaching  the  base  of  the  brain.  Here  they 
make  a  sharp  turn  recognizable  as  the  corpora  albicantia, 
and  end  in  the  optic  thalami. 

The  hippocampi  are  like  the  corpus  callosum  composed 
of  nerve  fibers  and  are  one  of  the  most  important  bands  of 
association  fibers  in  the  brain.  If  by  means  of  the  scalpel 
the  fornices  be  cut  and  this  entire  bit  of  nerve  fiber  matter 
lifted  off  or  folded  back  there  are  disclosed  two  large  bodies 
immediately  below  them  called  the  oplic  thalami.  The  optic 
thalami  lie  immediately  anterior  to  the  nates.  Between  the 
optic  thalami  lies  the  third  ventricle,  the  roof  which  is  there- 
fore practically  formed  by  this  band  of  nerve  fibers  just 
removed. 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         425 

The  continuation  of  the  third  ventricle  down  into  the 
infundibulum  is  now  apparent.  Running  across  the  third 
ventricle  from  one  side  to  the  other  may  be  seen  several 
commissures  serving  to  connect  the  sides.  The  attachment 
of  the  pineal  gland  to  the  optic  thalami  is  now  also  evident. 
From  the  blood-vessels  which  supply  the  brain  several 
arterial  branches  reach  the  third  ventricle  and  are  from  the 
third  ventricle  carried  through  the  foramina  of  Monro  into 
the  lateral  ventricles,  where  as  the  choroid  plexus  of  the 
brain  they  line  the  walls  of  these  ventricles  more  or  less 
completely  and  serve  to  nourish  them.  It  not  infrequently 
happens  that  these  delicate  blood-vessels  are  injured  and  a 
hemorrhage  of  the  brain  occurs,  inducing  apoplexy. 

If  an  incision  should  be  made  through  the  corpus  stria- 
turn  it  would  be  seen  to  be  divided  in  its  posterior  region 
into  an  inner  and  outer  portion  by  a  band  of  white  nerve 
fibers.  This  band  is  called  the  internal  capsule  and  consists 
of  a  large  number  of  nerve  fibers  which  are  on  their  way 
from  the  surface  of  the  cerebral  hemisphere  to  the  cord. 

The  Cranial  Nerves. 

Twelve  pairs  of  nerves  arise  from  the  base  of  the  brain, 
the  names  of  which  in  their  successive  order  and  the  distri- 
bution of  which  are  as  follows: 

First.  The  olfactory  nerve  passing  through  the  cribri- 
form plate  of  the  ethmoid  and  innervating  the  membrane  of 
the  nose.  It  is  the  nerve  of  smell.  It  differs  materially 
from  other  nerves  in  that  the  fibers  are  not  wrapped  up  into 
definite  nerve  trunks  by  a  connective  tissue  epineurium. 

Second.  The  optic  nerves  leading  to  the  eye  and  spread- 
ing out  there  in  the  retina.  They  are  wholly  sensory,  carry- 
ing the  visual  sensations  to  the  brain. 

Third.  The  motores  occult.  These  arise  from  the  crura 
cerebri  and  are  distributed  to  the  muscles  of  the  eye,  ex- 
cluding, however,  the  external  rectus  and  superior  oblique. 
They  are  motor  nerves  and  control  the  movements  of  the 
eye  which  these  muscles  produce.  In  addition  to  that,  fibers 


426  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

from  the  motores  occuli  reach  the  muscles  of  accommoda- 
tion and  the  muscles  of  the  iris.  It  is  this  latter  nerve 
which  in  a  reflex  way  causes  the  contraction  of  the  pupil 
when  the  eye  is  subjected  to  an  increased  amount  of  light. 
It  is  interesting  to  note  that  a  contraction  or  relaxation 
of  the  muscles  of  the  iris  is  never  confined  to  one  eye  alone, 
but  that  both  eyes  move  in  unison.  It  is  evident,  there- 
fore, that  the  motores  occuli  of  the  right  and  left  eye  are  in 
direct  anatomical  communication  with  each  other  at  or  near 
their  place  of  origin.  Fibers  from  this  same  nerve  control 
the  muscles  of  the  upper  eye-lid.  That  this  nerve  is  the 
most  important  motor  nerve  of  the  eye  may  be  readily  seen 
from  its  innervation,  and  a  section  of  the  nerve  induces  at 
once  the  relaxation  and  closing  of  the  upper  eye-lid ;  the 
impossibility  to  move  the  ball  of  the  eye,  a  dilatation  of  the 
pupil,  and  the  impossibility  of  a  contraction  of  the  same 
even  when  subjected  to  a  strong  light,  and  finally  a  paral- 
ysis of  the  accommodation  of  the  eye  so  that  the  focus  of 
the  eye  is  immovably  set  for  distant  objects. 

Fourth.  The  pathetici.  The  pathetici  leave  the  brain 
immediately  anterior  to  the  pons  Varolii,  innervate  the  su- 
perior oblique  muscles  and  so  help  to  control  the  move- 
ments of  the  eye  in  so  far  as  they  are  affected  by  these 
muscles.  The  cutting  of  the  patheticus  nerve  seems  to 
show  no  immediate  results  in  the  eye,  but  an  animal  so 
treated  is  unable  to  fix  its  gaze  upon  a  certain  point  when 
its  head  is  turned.  By  the  paralysis  of  the  superior  oblique 
muscle  the  eyeball  affected  is  rotated  along  with  the  head. 
In  this  way  the  two  eyes  are  not  directed  to  the  same  point 
and  a  double  vision  occurs. 

Fifth.  The  trigeminales .  The  fifth  pair  of  nerves,  the 
trigeminales,  contain  both  motor  and  sensory  fibers.  They 
arise  from  the  medulla  each  in  two  roots,  the  smaller  of 
which  contains  the  motor  fibers  which  arise  from  centers  in 
the  floor  of  the  fourth  ventricle,  while  the  larger  is  sensory. 
This  larger  root  before  joining  the  motor  one  passes 
through  the  large  Gasscrian  ganglion.  The  sensory  fibers 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         427 

arise  in  a  number  of  scattered  places  in  the  medulla,  and  in 
this  way  are  brought  into  direct  communication  with  quite 
a  number  of  different  centers  and  fibers.  After  the  passage' 
of  the  sensory  branch  through  the  Gasserian  ganglion  it 
unites  with  the  motor  branch  to  form  the  main  trunk.  This 
trunk,  however,  soon  divides  into  three  main  branches, 
hence  the  name  of  the  nerve,  which  in  a  general  way  are 
distributed  as  follows:  a.  The  ophthalmic  branch  going  to 
the  muscles  and  skin  of  the  forehead  and  upper  eyelid,  and 
the  mucous  membrane  of  the  nose.  b.  The  superior  max- 
illary  branch  innervating  the  skin  of  the  temples,  the  cheeks 
and  the  angle  of  the  mouth  and  upper  teeth,  and  within  the 
mouth  the  mucous  membrane  or  pharynx  and  soft  palate. 
c.  The  inferior  maxillary,  distributed  to  the  side  of  the 
head,  the  external  ear,  the  skin  of  the  lower  part  of  the 
face,  the  lower  teeth,  the  salivary  glands,  the  top  of  the 
tongue  and  the  muscles  which  move  the  lower  jaw  in  the 
process  of  mastication. 

While  anatomically  it  is  thus  divided  into  three  branches 
physiologically  it  contains  quite  a  number  of  different  kinds 
of  nerves  as  follows:  (1)  Sensory  nerves.  It  is  the  sen- 
sory nerve  for  the  dura  mater,  for  the  skin  of  the  entire 
face,  for  the  orbit  of  the  eye  as  well  as  the  ball  of  the  eye, 
for  the  nose,  the  mouth,  the  top  of  the  tongue,  the  gums, 
the  teeth,  the  surface  of  the  ear  and  the  auditory  meati.  In 
a  word,  by  means  of  this  nerve  the  sensation  of  touch  is 
made  possible  in  all  the  regions  mentioned.  (2)  Motor 
fibers.  It  innervates  the  muscles  of  mastication,  a  muscle 
of  the  soft  palate  and  the  tensor  muscle  of  the  midde  ear. 
(3)  Secretory  fibers  to  the  lachrymal  glands,  arousing 
these  to  the  secretion  of  the  tears.  (4)  Gustatory  nerves 
which  are  distributed  to  the  tongue.  This  function  is  de- 
nied by  some  observers,  but  it  is  probable  that  the  sensations 
of  sweet  and  sour  at  the  tip  of  the  tongue  are  carried  by  this 
nerve.  (5)  Vaso-motor  fibers  for  the  blood-vessels  of  the 
eye,  the  gums  and  the  tongue,  by  means  of  which  the  vas- 
cular supply  of  these  structures  is  to  a  certain  extent  con- 


428  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

trolled.  (6)  Reflex  nerves;  that  is,  nerve  fibers  which  by 
a  reflex  action  bring  about  the  involuntary  closing  of  the 
eyelid,  such  as  winking,  or  which  cause  coughing  and 
sneezing,  or  the  involuntary  movements  of  swallowing  when 
the  soft  palate  is  stimulated.  (7)  Fibers  which  in  a  reflex 
way  bring  about  not  muscular  contractions,  as  in  number  6, 
but  secretions  of  saliva  or  tears,  occasioned  by  the  stimula- 
tion respectively  of  the  mucous  membrane  of  the  mouth  or 
an  irritation  of  the  conjunctiva  of  the  eye. 

Sixth.  The  abducentes.  The  abducentes  nerves  arise 
from  the  medulla  and  are  distributed  to  the  external  recti  of 
the  eyes  controlling  their  movements.  The  sectioning  of 
this  nerve  causes  a  turning  of  the  affected  eyeball  inwards. 

Seventh.  The  faciales.  The  faciales  or  facial  nerves 
arise  on  the  floor  of  the  fourth  ventricle  and  are  distributed 
mainly  to  the  muscles  of  the  face.  It  is,  therefore,  almost 
wholly  a  motor  nerve  and  is  of  special  importance  from  the 
fact  that  it  is  the  nerve  which  controls  the  muscles  of  ex- 
pression and  mimicry. 

Eighth.  The  acoustid.  The  nerves  acoustici  or  audi- 
tory nerves  have  their  origin  in  centers  in  the  floor  of  the 
fourth  ventricle  of  the  medulla  and  innervate  the  inner  ear. 
They  are  sensory  and  carry  to  the  brain  the  sensations  of 
sound. 

Ninth.  The  glossopharyngcah.  The  glossopharyngeal 
nerves  are  the  nerves  of  taste  and  are  distributed  mainly  to 
the  posterior  portions  of  the  tongue.  Fibers,  however, 
reach  the  tip  of  the  tongue  as  well,  which  fibers  are  be- 
lieved by  some  physiologists  to  cause  the  sensation  of  bitter 
at  this  point.  The  sensations  of  sweet  and  sour  are  by 
these  same  investigators  referred  to  the  trigeminal  nerve. 
On  the  back  of  the  tongue,  however,  the  glossopharyn- 
geal nerves  are  able  to  carry  sensations  of  sweet  and  sour 
as  well.  They  also  innervate  the  mucous  membrane  of  the 
back  of  the  nose  and  the  pharynx.  They  contain  a  few  mo- 
tor fibers  for  certain  muscles  of  the  pharynx,  and  send  to  the 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         429 

parotid  gland  the  nerves  which  control  the  secretion  of  the 
same. 

Tenth.  The  vagi.  The  vagi  or  pneumogastrics  are  the 
longest  of  the  cranial  nerves  and  their  distribution  widest. 
They  send  branches  to  the  pharynx,  gullet,  larynx,  wind- 
pipe, lungs,  heart,  stomach,  and  even  read;  the  solar  plexus 
in  the  mesentery.  They  contain:  First. — Motor  fibers  for 
the  muscles  of  the  pharynx,  oesophagus  and  larynx,  for  the 
muscular  coat  of  the  stomach  and  the  muscles  of  the  princi- 
pal portion  of  the  small  intestine.  Second. — Inhibitory  fibers 
for  the  heart.  Third. — Sensory  fibers  for  the  throat,  the 
oesophagus  and  lungs.  Fourth. — Reflex  fibers  which  affect 
the  process  of  inspiration  and  expiration.  FiftJi. — In  man, 
finally,  it  contains  the  depressor  nerve  (separate  in  the 
rabbit)  which  runs  from  the  heart  to  the  brain  and  carries 
sensory  impulses  to  the  brain.  This  depressor  figures  inte- 
grally in  the  vascular  supply  of  the  body. 

Eleventh.  The  accessorii.  The  spinal  accessory  nerves 
in  reality  arise  from  the  cervical  portion  of  the  spinal  cord, 
but  run  into  the  skull  alongside  of  the  spinal  cord,  receiv- 
ing a  few  fibers  from  the  medulla  and  then  pass  out  with 
the  pneumogastric  nerves.  Bach  gives  off  a  branch  to  the 
pneumogastric  nerve,  while  the  main  portion  of  the  trunk 
is  distributed  to  the  muscles  of  the  shoulder. 

T^velfth.  The  hypoglossi.  The  hypoglossal  nerves  are 
the  motor  nerves  of  the  tongue  and  innervate  all  of  the 
muscles  of  the  same.  They  carry,  however,  a  few  sensory 
and  vaso-motor  fibers  to  the  tongue.  This  nerve  is  of  espe- 
cial interest  in  the  consideration  of  the  process  of  mastica- 
tion, and  better  still  in  the  production  of  articulate  speech. 

The  Sympathetic  System. 

The  sympathetic  system  consists  of  two  chains  of  ganglia 
lying  alongside  the  backbone  and  easily  visible  when  the 
chest  and  abdominal  viscera  are  removed.  Each  chain  con- 
sists of  twenty-four  ganglia.  In  the  coccygeal  region  the 
two  chains  meet  in  a  median  -  placed  ganglion,  making, 


430  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

therefore,  the  total  number  of  sympathetic  ganglia  twenty- 
four  pairs  and  one;  that  is,  forty-nine  ganglia.  The  gan- 
glia on  each  side  are  connected  with  each  other  by  means 
of  nerves,  while  the  first  ganglion  in  the  cervical  region  is 
connected  in  turn  with  the  brain. 

In  addition  to  the  connections  which  each  ganglion  has 
with  the  one  preceding  and  the  one  following,  two  other 
nerves  arise  from  it.  One  of  these  is  the  communicating 
branch  already  referred  to  in  the  description  of  the  spinal 
cord,  a  branch  by  means  of  which  the  sympathetic  ganglion 
is  anatomically  connected  with  the  spinal  cord.  The  other 
is  the  visceral  nerve  proper,  the  nerve  trunk  distributed  to 
the  viscera,  carrying  to  the  same  the  impulses  of  this  cen- 
tral ganglion,  or  conveying  to  these  ganglia  impulses  from 
the  viscera.  A  very  important  nerve  of  this  kind  is  the 
sympathetic  nerve  which  reaches  the  heart  and  is  already 
familiar  as  the  cardio-accelerator.  The  visceral  branches 
of  a  number  of  abdominal  ganglia  unite  to  form  a  common 
nerve  trunk  on  each  side  called  the  splanchnic  nerve.  This 
nerve  is  distributed  to  the  abdominal  viscera  through  the 
solar  plexus  in  the  mesentery. 

The  term  sympathetic  is  a  rather  unfortunate  one,  as  it 
frequently  leads  to  the  impression  that  it  is  mainly  concerned 
with  phenomena  to  which  the  somewhat  vague  term  of  sym- 
pathy is  applied.  That,  to  use  a  stereotyped  expression,  it 
keeps  one  part  of  the  body  in  sympathy  with  another. 
Such  an  expression  is,  of  course,  from  a  scientific  standpoint 
perfectly  meaningless.  If  the  term  " visceral"  system  could 
be  generally  applied  to  it  this  misinterpretation  might  be 
avoided,  while  at  the  same  time  the  term  "visceral"  would 
give  a  clue  to  the  function  of  this  system  which  is  in  a 
general  way  concerned  with  the  physiological  activities  of 
the  visceral  organs. 

General  Histology. 

Having  in  the  previous  paragraphs  called  attention  to 
the  systems  as  a  whole  and  their  relation  to  each  other,  the 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         431 

next  step  is  to  study  in  detail  the  individual  units  of  which 
these  systems  are  composed. 

The  unit  by  the  multiplied  arrangements  of  which  the  en- 
tire structure  of  the  nervous  system  is  built  up  is  called  the 
neuron.  A  neuron  is  a  nervous  cell  together  with  the  nerves 
running  out  from  it.  By  this  name,  therefore,  is  included 
not  the  nerve  cell  merely,  but  the  nerve  fiber  as  well.  It 
has  the  advantage  of  doing  away  with  that  arbitrary  dis- 
tinction between  nerve  cells  and  nerve  fibers,  and  gives  em- 
phasis to  the  fact  that  a  nerve  cell  with  the  fibers  springing 
from  it  is  a  unit  physiologically  as  well  as  anatomically. 

But  the  value  of  this  name  is  further  increased  by  the 
fact  that  all  the  neurons  in  the  entire  nervous  system  are 
supposed  to  be  distinct  and  independent  anatomically  and 
possibly  to  some  extent  physiologically.  A  neuron  is  to  the 
nervous  system  what  a  single  citizen  is  to  the  state.  In 
fact,  recent  researches  show  that  the  different  neurons  of 
the  body  are  not  in  direct  anatomical  continuity,  but  that 
each  is  an  anatomical  entity,  and  that  impulses  from  one 
neuron  to  the  other  can  be  sent  only  by  having  one  neuron 
act  as  a  stimulus  in  arousing  a  new  impulse  in  the  second. 
It  is  not  the  simple  original  impulse  that  can  reach  the  sec- 
ond neuron,  any  more  than  in  two  persons  joining  hands  is  it 
the  pain  experienced  by  one  that  is  transmitted  to  the  other. 
The  first  as  a  stimulus  must  reproduce  the  same  pain  in  the 
second  anew.  The  relative  arrangements  and  the  super- 
position of  the  various  neurons  of  the  central  nervous  system 
will  be  discussed  further  on  in  this  chapter,  it  being  the 
point  here  to  treat  of  their  general  histology  merely. 

Neurons. 

One  of  the  most  remarkable  things  about  a  neuron  is 
usually  its  size.  While  there  are  neurons  lying  within  the 
central  nervous  system  only  a  few  centimeters  or  less  in 
length,  there  are,  on  the  other  hand,  neurons  having  a 
length  of  several  feet.  Such  neurons,  for  instance,  as  reach 
from  the  cortex  of  the  brain  to  the  lumbar  cord,  or  still 


432 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


others  reaching  from  the  spinal  cord  to  the  ends  of  the 
extremities.  Anatomically  neurons  are  classed  on  the  basis 
of  the  number  of  nerves  issuing  from  the  cell  body.  A 
nervous  cell  with  a  single  nerve  fiber  issuing  from  it  is 
spoken  of  as  mono-neuric.  These  mono-neuric  cells  are, 
however,  physiologically  really  di-neuric,  the  single  nerve 
containing  passages  leading  towards  the  cell  and  away  from 

it,  and  so  being  practically 
the  same  as  two  separate 
nerves.  The  usual  type  is 
the  di-neuric  neuron. 

More  than  two  nerves, 
however,  may  arise,  in 
which  case  the  neuron  is 
spoken  of  as  poly-neuric. 
Illustrations  of  di  -  neuric 
neurons  may  be  found  in 
such  ganglia  as  the  spinal 
root  ganglia,  in  which  a 
nerve  runs  to  each  cell  body 
and  a  second  nerve  away 
from  it.  Usually  one  of  the 
fibers  or  extensions  of  the 
cell  body  becomes  a  typi- 
cal nerve,  while  the  other 
branches  sub-divide  repeat- 
edly and  form  a  perfect 
network  of  smaller  fibrils 
reaching  out  in  various  di- 
rections. Such  branched  terminations  are  spoken  of  from 
their  resemblance  to  trees  as  dendrons.  These  dendrons  do 
not  reach  to  distant  points  like  the  nerve  does  to  skin,  mus- 
cles or  sense-organs,  but  seem  to  terminate  among  the  neigh- 
boring cells  and  it  is  believed  that  impulses  from  one  cell  to 
another  are  carried  by  dendrons  of  these  contiguous  nerves. 
A  neuron,  therefore,  consists  essentially  of  two  parts; 
the  cell  body  and  its  extensions  into  nerves  and  dendrons. 


Figf.     138.— A     POLY-NEURIC     GANGLION     CELL. 

(After  Gegenbaur.) 

Dotted  line  indicates  the  main  axis-cylin- 
der. 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.          433 

The  cell  body  is  usually  much  larger  than  that  of  other  cells 
in  the  body  and  is  composed  of  granular  protoplasm  contain- 


Fig.   139. — TWO  CORPUSCLES  OF  PURKINJE  FROM  THE    CEREBELLUM    SHOWING  THEIR  IN- 
VESTMENT   WITH    DENDRONS    FROM    CELLS    OF    THE    OUTER    GRAY    MATTER.       (After 

Ramon  y  Cajal.) 

a,  axis-cylinder  of  corpuscle  of  Purkinje;  &,  network  of  dendrons. 

ing  a  relatively  large  nucleus.  The  cell  body  is  really  the 
center  of  energy.  We  must  imagine  that  here,  in  some 
chemical  way  no  doubt,  energy  is  liberated  which  takes  the 
form  of  nervous  activity.  That  such  a  breaking  down  of 
the  substance  of  nerve  cells  occurs  when  they  are  being 
stimulated  has  been  satisfactorily  proved  by  experiments  in 
which  nerve  cells  were  subjected  to  long  continued  stimuli, 
then  examined  with  a  microscope  and  compared  with  similar 
cells  not  so  stimulated.  Such  stimulated  cells  shrink  in 
volume,  and  in  the  plainest  way  indicate  a  severe  loss  of 
their  substance.  The  nucleus  becomes  much  smaller. 
Similar  observations  have  been  made  on  old  nerve  cells. 
Here,  too,  the  cell  body  becomes  shrunken  and  the  nucleus 
practically  disappears.  Sometimes  the  cell  body  may  dis- 
appear altogether. 

The  Nerves. 

While  in  a  direct  sense  the  term  "nerve"  might  include 
the  dendrons  it  is  more  usually  referred  to  the  main  fiber 
leading  from  the  cell  to  muscle,  skin,  sense-organ,  or  other 
neurons.  If  such  a  nerve  be  examined  a  little  distance 

28 


434 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


away  from  the  center  from  which  it  originated,  it  seems  in 
a  fresh  condition  almost  homogeneous,  but  when  allowed  to 
stand  or  treated  with  proper  re-agents  it  soon  resolves  itself 
into  three  structures. 

Axis-  Cylinder.  Running  through  the 
center  of  the  nerve  fiber  as  a  continuation 
of  the  nerve  cell  itself  is  the  axis-cylin- 
der. This  is  the  real  nerve  matter  of  the 
fiber,  and  is  the  only  one  that  is  really 
physiologically  concerned  in  the  carrying 
of  nervous  impulses.  In  fact,  the  two 
other  coats  may  sometimes  be  absent  alto- 
gether, but  an  axis-cylinder  can  never  be 
absent. 

Medullary  Sheath.  Surrounding  the 
axis-cylinder  is  a  thick  whitish-looking 
coat  called  the  medullary  sheath.  This 
medullary  sheath  seems  interrupted  at  in- 
tervals of  about  one-twenty-fifth  of  an 
inch,  which  interruptions  are  called  the 
nodes  of  Ranvier.  The  medullary  coat 
between  two  consecutive  nodes  contains  a 
large  nucleus  and  gives  evidence  that  this 
inter-node  is  of  cellular  origin.  Chem- 
ically the  medullary  coat  consists  of  a 
substance  called  myelin,  a  substance 
somewhat  akin  to  that  derived  from  cer- 
tain connective  tissues. 


Fig.    140.  —  MEDULLATED 

NERVE-FIBER     TREATED 

WITH  OSMIC  ACID.  (After 
Key  and  Retzius.) 


Primitive  Sheath.     Around  the  med- 
ullary coat  in  turn  is  a  thin  epithelial  coat 

E,  node  of  Ranvier;  K,  11      i    ,1  •  1         ,  t 

nucleus  of  medullary    called  the  primitive  sheath  or  neurolem- 


and    ax 

show. 


primitive  sheath    ma    or  by  others  the  sheath  of  Schwann. 

is  -  cylinder    also 

The  medullary  coat  ceases  near  the  cell 
from  which  the  axis-cylinder  arises,  but  the  primitive  sheath 
is  usually  continued  over  the  cell  body  itself.  This  sheath 
further  dips  down  into  the  nodes  of  Ranvier. 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM.          435 

Two  opposing  views  are  prevalent  as  to  the  nature  of 
the  axis-cylinder.  According  to  one  view  this  cylinder 
consists  of  a  bundle  of  still  finer  fibrillae,  too  small  to  be 
resolved  by  the  microscope,  and  along  these  fine  fibrillae  the 
nervous  impulses  are  supposed  to  pass.  The  presence  of 
many  such  fibrillae  in  a  single  axis-cylinder  would  explain 
how  a  single  nerve  fiber  might  branch  near  its  termination, 
as  many  do.  By  others  the  axis-cylinder  is  looked  upon  as 
a  tube  of  nervous  plasm,  through  which  the  nervous  impulse 
finds  its  way,  and  the  branching  of  the  nerve  fibers  is  ex- 
plained in  the  same  way  as  the  terminal  branchings  of  a 
water-main. 

The  medullary  sheath  forms  soon  after  the  appearance 
of  the  axis-cylinder  and  arises  from  certain  cells  which  sur- 
round the  axis-cylinder  much  like  a  string  of  spools  would 
surround  a  wire  passing  through  them.  The  substance  of 
these  enclosing  cells  after  they  have  elongated  is  changed 
into  myelin,  retaining,  however,  its  nucleus.  The  divisions 
between  contiguous  cells  is  still  indicated  by  the  nodes  of 
Ranvier. 

While  the  matter  of  origin  of  the  medullary  sheath  is, 
therefore,  fairly  clear  we  are  almost  entirely  at  sea  for  its 
physiological  explanation.  That  it  serves  as  a  kind  of  insu- 
lation for  the  nervous  impulse  somewhat  like  the  silk  around 
a  copper  wire  seems  hardly  true.  There  is  nothing  to 
warrant  such  a  belief.  That  it  may  serve  as  a  protection 
against  changes  of  temperature,  and  possibly  even  in  a 
mechanical  way,  may  be  true  in  some  cases  but  would  hardly 
explain  the  existence  of  a  medullary  sheath  in  the  brain  or 
spinal  cord  itself  where  fluctuations  of  temperature  certainly 
do  not  occur.  The  statement  that  nerves  do  not  become 
functional  until  the  medullary  coat  is  developed  does  not 
necessarily  mean  that  the  function  depends  upon  this  coat. 
It  may  simply  mean  that  the  axis-cylinder  becomes  func- 
tional about  the  same  period  that  the  medullary  sheath 


436  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

appears.  Until  further  light,  therefore,  is  thrown  upon  the 
subject  we  must  look  upon  this  coat  as  practically  unex- 
plained. 

Gray  Fibers. 

Not  all  nerve  fibers  possess  the  medullary  coat.  The 
majority  of  the  fibers  of  the  sympathetic  system  are  devoid 
of  it  as  well  as  a  number  of  cerebro-spinal  nerves. 

As  the  medullary  coat  is  white  it  gives  when  present  the 
white  appearance  to  the  fiber,  and  for  this  reason  medul- 
lated  fibers  are  frequently  referred  to  as  white  fibers.  The 
absence  of  the  coat,  however,  allows  the  gray  color  of  the 
axis-cylinder  to  appear,  and  for  this  reason  non-medullated 
fibers  are  usually  referred  to  as  gray  fibers.  It  is  well  to 
bear  in  mind,  however,  that  this  is  a  purely  arbitrary  dis- 
tinction depending  wholly  upon  an  accidental  covering  and 
refers  in  no  way  to  differences  in  the  nervous  matter  itself. 

Nerve  Trunks. 

Nerve  fibers  do  not  as  a  rule  run  singly,  but  are  col- 
lected into  large  bundles  familiar  as  nerve  trunks.  Ex- 
amples of  such  nerve  trunks  may  be  the  sciatic  nerve  or 
optic  nerve ;  in  fact  any  of  those  whitish  threads  which  in 
ordinary  dissection  appear  as  nerves.  Such  trunks  are 
easily  recognized  as  nerve  trunks  by  their  whitish  appear- 
ance ;  but  this  whitish  appearance  is  really  due  to  the  con- 
nective tissue  which  is  wrapped  around  the  enclosed  fibers. 
A  cross-section  of  a  nerve  trunk  would  reveal  about  the 
following  general  arrangement: 

The  individual  nerve  fibers  are  grouped  in  from  one  to 
many  definite  bundles  called  funiculi.  Bach  funiculus  is 
closely  invested  in  a  coat  of  connective  tissue  called  the 
perineurium,  while  branches  from  this  perineurium  extend 
into  the  funiculus  supporting  more  or  less  completely  the 
individual  fibers  and  forming  the  endoneurium.  These 
funiculi  are  then  together  wrapped  in  a  common  coat  of 
connective  tissue  passing  all  around  them  and  between 
them  called  the  epineurium.  Through  these  connective 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.          437 

tissue  coverings  blood-vessels  and  lymphatics  find  their  way 
as  through  other  tissues.     Along  the   course  of  the  nerve 


Fig.  141.— SECTION  OF  A  NERVE  TRUNK  (HUMAN).    (After  Schafer.) 
ep,  epiueurium;  per,  perineurium;  end,  endoneurium ;   v,  blood-vessels;   f,  fat  cells 
stained  with  osniic  acid. 

trunk  funiculus  after  funiculus  is  given  off  as  a  separate 
branch,  and  finally  the  individual  funiculus  is  separated 
until  at  the  end  of  the  nerve  trunk  this  separation  is  ex- 
tended to  the  nerve  fibers  themselves. 

The  Development  of  Nerves. 

One  of  the  most  interesting  chapters  in  embryology  is 
the  development  of  the  nervous  tissues  and  the  organs  de- 
rived from  them.  Such  study  shows  that  the  nervous  cells 
are  derived  from  peculiar  cells  called  neuroblasts,  which 
cells  by  their  amoeboid  movements  are  able  to  place  them- 
selves in  definite  positions  through  the  body  and  then  later, 
by  a  kind  of  polarization,  are  able  to  determine  the  direc- 
tion of  the  nerves  issuing  from  them.  When  one  is  re- 


438  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

minded  of  the  innumerable  number  of  nerve  cells  compos- 
ing the  nervous  system,  of  their  intimate  inter-relation,  and 
yet  at  the  same  time  of  the  definite  way  in. which  they  are 
connected  by  their  fibers,  one  can  appreciate  the  precision 
with  which  these  primitive  neuroblasts  must  have  distrib- 
uted themselves  while  determining  their  direction  of  growth. 
In  fact,  there  are  not  lacking  physiologists  who  believe  that 
forms  of  nervous  derangement,  from  insanity  downwards, 
are  due  to  possible  accidental  misplacements  and  malforma- 
tions of  these  primitive  neuroblasts. 

A  second  interesting  point  concerning  these  neuroblasts  is 
that  they  do  not  increase  in  number  after  about  the  third  or 
fourth  month  of  fcetal  life,  and  that  the  entire  development 
of  the  nervous  system  following  that  is  due  to  an  expan- 
sion of  already  formed  neurons  and  the  establishment  of 
more  and  more  complicated  channels  of  connection. 

Possibly  the  most  important  fact  from  a  teacher's  stand- 
point to  remember,  is  that  the  development  of  these  channels 
of  association,  these  anatomical  connections  between  differ- 
ent neurons,  is  not  completed  until  up  to  and  even  past 
maturity,  and  explains  the  physiological  impossibility  for 
the  existence  of  nervous  or  mental  faculties  in  the  young 
which  later  on  will  naturally  appear. 

The  Regeneration. 

When  a  nerve  is  cut,  the  end  of  the  nerve  fiber  severed 
from  the  cell  body  to  which  it  belonged  disintegrates,  and 
a  new  nerve  fiber  to  innervate  the  place  of  the  old  arises  as 
an  outgrowth  from  the  stump  of  the  end  in  connection  with 
the  cell.  If,  however,  the  severed  ends  of  such  a  nerve  be 
connected  they  seem  soon  to  have  grown  together.  This 
growing  together  does  not,  however,  affect  the  axis-cylin- 
der, for  the  axis-cylinder  grows  down  through  the  coats  of 
the  old  nerve  not  unlike  the  growing  of  a  rootlet  through 
the  soil.  In  this  growth  it  is  no  doubt  guided  by  the  path 
of  the  old  fiber  itself,  with  the  medullary  coat  and  primitive 
sheath  of  which,  contact  seems  to  have  been  made. 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         439 

Such  a  regeneration  of  fibers  does  not  differ  in  any  way 
from  the  manner  in  which  nerve  fibers  arise  in  the  embryo. 
The  spinal  nerves  grow  out  from  the  spinal  cord  and  pene- 
trate further  and  further  until  they  finally  reach  their  in- 
tended terminations.  The  optic  nerve  (together  with  the 
retina)  is  a  direct  outgrowth  of  the  brain.  The  auditory 
nerve  is  a  growth  from  the  brain,  which  finally  reaches  and 
connects  with  the  developing  ear. 

Neuroglia. 

Ill  the  brain  and  spinal  cord  where  the  neurons  are 
closely  packed  they  seem  to  be  supported  and  held  in  place 
by  a  peculiar  kind  of  connective  tissue  differing  entirely 
from  that  which  supports  other  tissues.  The  supporting 
tissue  here  consists  of  large,  many-branched  cells,  looking 
very  much  indeed  like  nerve  cells.  The  many  branches  of 
these  cells  seem  to  connect  and  form  a  supporting  mesh- 
work  for  the  more  delicate  nervous  tissue.  These  support- 
ing cells  and  the  network  which  arises  from  them  are  spoken 
of  as  the  neuroglia.  These  cells  are  not  connective  tissue 
cells,  but  are  in  origin  related  to  the  nervous  cells,  having 
been  derived  from  the  same  primitive  source.  In  sections 
of  the  spinal  cord  these  cells  may  be  easily  mistaken  for 
nerve  cells,  differing,  however,  from  them  in  the  absence  of 
all  nervous  functions  and  so,  of  course,  anatomically  in  the 
absence  of  nerves. 

GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM. 

Before  going  into  the  physiology  of  special  portions  of 
the  system  it  is  desirable  to  treat  of  those  physiological 
properties  which  all  nervous  tissues  have  in  common.  In 
fact,  the  specific  physiologies  of  the  special  portions  are  due 
more  to  the  origin  and  distribution  of  the  nerves  than  to 
any  physiological  difference  in  their  activities. 

The  general  physiology  of  a  nerve  may  be  summed  up  in 
the  statement  that  it  is  to  convey  a  nervous  impulse.  This 
impulse  may  arise  either  in  the  cell  of  which  the  nerve  is  a 


440  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

continuation,  and  from  this  be  carried  to  muscle  or  gland, 
or  else  in  some  sense-organ  to  be  carried  inwards  to  the 
appropriate  center.  This  brings  up  the  question,  in  what 
manner  a  nerve  may  be  stimulated  to  transmit  such  im-. 
pulses. 

Nerve  Stimuli. 

In  the  laboratory  it  is  possible  to  stimulate  a  nerve  arti- 
ficially in  the  following  ways : 

1. — By  Mechanical  Stimuli.  A  tap,  a  pinch  or  blow  on 
a  living  exposed  nerve  excites  it  and  is  the  occasion  of  an 
impulse  through  the  nerve.  A  familiar  illustration  of  this 
is  found  in  striking  the  crazybone  at  the  elbow,  which  is 
in  reality  striking  the  nerve  at  this  point.  The  blow  occa- 
sions an  impulse  which  runs  to  the  brain,  and  by  the  brain 
is  referred,  although  erroneously,  to  the  fingers. 

2. — Thermal  Stimuli.  Sudden  change  in  the  tempera- 
ture excites  the  nerve,  be  the  change  upward  or  downward. 
If  this  change,  however,  is  very  gradual,  the  nerve  seems 
to  be  able  to  accustom  itself  to  the  change  and  no  direct 
impulse  arises. 

3. — Chemical  Stimuli.  Quite  a  number  of  substances 
chemically  alter  a  nerve  fiber  and  so  stimulate  it.  Thus 
immersing  the  end  of  a  nerve  in  a  strong  solution  of  com- 
mon salt  excites  it.  Here,  too,  if  such  a  nerve  be  placed  in 
a  very  dilute  solution  and  this  solution  then  gradually  made 
more  concentrated  no  excitation  follows. 

4. — Electrical  Stimuli.  One  of  the  most  satisfactory 
ways  to  stimulate  a  nerve  in  experimental  physiology  is  by 
means  of  the  electrical  current.  An  electric  shock  passing 
through  a  nerve  fiber  at  any  part  along  its  course  power- 
fully excites  it.  Even  a  sudden  change  in  the  strength  of 
the  current  through  a  nerve  excites  it.  A  steady  current, 
however,  has  no  effect,  but  when  such  a  current  is  suddenly 
broken,  the  sudden  disappearance  of  the  ciirrent  acts  as  a 
stimulus. 

The  explanation  of  all  these  stimuli  lies  in  the  siidden- 
ness  with  which  any  change  is  brought  about  in  the  nerve 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.          441 

fiber,  be  this  sudden  "change  electrical,  thermal,  mechanical 
or  chemical.  Of  course  the  stimuli  so  far  enumerated  are 
all  artificial  stimuli  which  in  the  normal  physiology  of  the 
body  are  never  called  into  play.  The  natural  nerve  stimuli 
are  of  two  kinds: 

First,  stimuli  which  arise  in  the  nerve  centers  in  a  way 
so  far  entirely  unexplained.  These  are  stimuli  which  are 
produced  in  the  nerve  cells  themselves  and  by  these  sent 
out  along  the  fibers.  Such  stimuli  are  those  produced  by 
the  cells  of  the  cortex  of  the  brain,  which  produce  the  con- 
traction of  the  fingers  or  toes.  They  may  be  spoken  of 
as  central  stimuli.  These  are  always  called  into  play  in  the 
production  of  motor  impulses. 

The  second  kind  is  peripheral  stimuli  which  are  best  ex- 
hibited in  the  organs  of  special  sensation.  Thus  in  the  eye, 
light  in  some  way  excites  the  optic  terminations  in  the  ret- 
ina. In  the  ear  vibrations  in  the  cochlea  excite  the  audit- 
ory hairs  on  the  basilar  membrane,  while  on  the  skin  gen- 
erally, foreign  bodies  in  their  effect  upon  the  tactile  cor- 
puscles usually  occasion  a  stimulus  interpreted  in  the  mind 
as  sensations  of  touch. 

These  peripheral  stimuli  are,  however,  not  limited  to  the 
special  sense-organs.  Such  stimuli  may  originate  in  any 
part  of  the  body.  In  the  stomach  the  presence  of  food  may 
produce  a  stimulus  which  is  carried  to  the  brain,  and  there 
in  a  reflex  way  translated  into  a  motor  impulse  to  move  the 
muscles  of  the  stomach.  In  fact,  it  will  be  pointed  out  that 
the  special  sense-organs  are  nothing  more  than  contrivances 
by  means  of  which  stimuli  which  are  too  feeble  to  excite 
nerves  in  general  are  so  manipulated  in  a  specially  con- 
structed sense-organ  as  to  make  possible  such  an  excita- 
tion. 

Do  Nervous  Impulses  Differ  Among  Themselves? 

Some  nerves  carry  motor  impulses,  others  tactile  im- 
pulses, still  others  visual  impulses,  and  the  question  natur- 
ally arises  do  these  impulses  differ  inter  se? 

The  older  physiologists  entertained  the  view  that  the 
different  results  produced  by  different  impulses  were  due  to 


442  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

these  impulses  themselves.  That  the  sensation  of  sight 
was  produced  by  the  optic  nerve  as  such,  and  that  a  muscle 
contracted  in  obedience  to  a  peculiar  motor  nervous  im- 
pulse. Soon  after,  this  very  sweeping  distinction  was  nar- 
rowed down  to  a  disvision  into  two  kinds  of  nervous  im- 
pulses— those  which  produced  motion  and  those  which  re- 
sulted in  sensation.  That  such  impulses  were  inherently 
different  was  occasioned  by  the  observation  that  when  a 
motor  nerve  was  cut  and  the  end  connected  with  the  muscle 
pinched  a  contraction  followed,  but  that  when  the  central 
end  was  pinched  no  sensation  followed.  While  on  the  other 
hand,  when  the  sensory  nerve  was  cut,  no  motion  resulted 
upon  the  distal  end  being  pinched,  but  a  decided  sensation 
followed  the  stimulation  of  the  central  end.  There  is,  how- 
ever, every  reason  to  believe  that  these  impulses  do  not  dif- 
fer among  themselves,  but  that  the  difference  in  results  is 
due  to  the  different  endings  which  these  nerves  have.  A 
sensory  nerve  cannot  produce  motion  for  the  simple  reason 
that  it  is  not  in  contact  with  muscles,  while  a  motor  nerve 
cannot  produce  sensation  for  the  simple  reason  that  it  does 
not  run  to  centers  where  such  sensations  are  received. 

That  all  nerve  fibers  are  physiologically  alike  seems 
further  evident  from  the  following  reasons:  (1.)  A  micro- 
scopic and  chemical  analysis  shows  no  differences  whatever 
between  the  nerve  fibers.  (2.)  All  nerve  fibers  carry  im- 
pulses in  both  directions.  For  instance,  when  a  nerve  is 
stimulated  in  the  middle  of  its  course  the  impulse  runs  from 
this  point  towards  both  ends  with  equal  facility  and  rapidity, 
and  this  is  true  whether  the  nerve  be  a  sensory  or  a  motor 
one.  (3.)  The  nature  of  the  nervous  impulse  seems  to  be 
the  same  no  matter  what  may  have  been  the  occasion  for 
its  excitation.  Thus  a  nervous  impulse  resulting  from  the 
pinching  of  a  nerve  is,  as  far  as  we  are  able  to  detect,  per- 
fectly identical  with  the  impulses  produced  by  an  electric 
current,  or  even  by  the  natural  end  organ  itself.  Thus,  the 
impulse  which  runs  along  the  optic  nerve,  regularly  occa- 
sioned by  light  falling  on  the  retina,  is  identical  with  the 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM.          443 

impulse  carried  by  the  optic  nerve  when  this  nerve  is  elec- 
trically stimulated. 

Having  now  seen  the  oneness  of  all  nervous  impulses 
the  question  arises,  what  is  its  nature? 

The  Nature  of  a  Nervous  Impulse. 

Soon  after  the  electrical  current  became  known  many 
attempts  were  made  by  the  older  physiologists  to  explain 
nervous  impulses  in  terms  of  electricity.  The  analogy 
between  the  nerves  of  the  body  and  a  system  of  telephone 
or  telegraph  wires  was  too  striking  to  be  overlooked.  But 
all  attempts  to  explain  one  in  terms  of  the  other  have  so 
far  been  a  failure.  That  a  nervous  impulse  is  not  of  an 
electrical  nature  is  evident  for  several  reasons:  A  nervous 
impulse  will  not  travel  along  a  dead  nerve,  or  even  a  nerve 
which  has  been  numbed  by  cold.  A  nervous  impulse  will 
not  pass  across  a  cut  in  a  nerve,  even  though  the  two  cut 
ends  be  fastened  together.  Surely  if  nervous  impulses  were 
of  an  electrical  nature  they  would  still  pass  in  spite  of  these 
difficulties.  It  has  been  possible  to  measure  the  rate  at 
which  nervous  impulses  move.  This  measurement  was  first 
accomplished  by  the  physiologist  Helmholtz.  The  experi- 
ment is  simple  enough.  A  muscle  was  cut  out  from  the 
body  of  an  animal  and  a  long  portion  of  the  nerve  leading 
to  it  left  intact.  The  muscle  and  nerve  preparation  were  so 
arranged  that  the  time  could  be  very  accurately  measured 
between  the  moment  when  the  nerve  was  stimulated  and  the 
moment  when  the  muscle  contracted.  The  nerve  was  now 
stimulated  close  to  its  insertion  in  the  muscle,  and  the  time 
that  elapsed  between  the  stimulation  of  the  nerve  and  the 
contraction  of  the  muscle  carefully  observed.  Next,  the 
nerve  was  stimulated  at  its  further  end,  that  is,  the  nervous 
impulse  had  now  to  go  further  through  the  nerve  than  it  did 
in  the  first  instance.  Again  the  time  elapsing  between  the 
moment  of  stimulation  and  the  moment  of  contraction  was 
noted.  The  difference  in  time  was  of  course  the  extra  time 
needed  in  the  second  case  for  the  impulse  to  traverse  the 
added  length  of  nerve. 


444  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

In  such  a  simple  way  the  experiment  proved  the  rapidity 
of  a  nervous  impulse  to  be  28  meters;  that  is,  a  little  over 
92  feet  per  second.  These,  however,  are  the  figures  for  the 
motor  nerves  of  the  frog.  The  rate  of  transmission  is  some- 
what faster  in  the  motor  nerves  of  warm-blooded  animals, 
and  is  here  probably  not  far  from  100  feet  per  second. 

Experiments  on  sensory  nerves  are,  of  course,  not  so 
easy,  but  there  is  reason  to  believe  that  the  speed  of  the 
impulse  is  about  the  same  as  that  of  the  motor  nerves. 
Such  a  speed  of  about  100  feet  per  second  is,  of  course, 
exceedingly  slow  compared  with  the  rate  of  transmission  of 
an  electric  impulse,  and  would  seem  to  settle  conclusively 
the  difference  between  the  two. 

That  a  nervous  impulse  is  of  a  chemical  nature  seems 
disproved  by  the  fact  that  no  exhaustion  occurs  in  a  nerve  in 
the  transmission  of  this  impulse.  It  has  been  possible  in 
experiments  to  send  long  continued  repeated  impulses  along 
a  nerve  without  noticing  at  the  close  of  the  experiment  that 
the  nerve  had  been  thereby  exhausted.  Such  stimulation  of 
course  commonly  exhausts  the  muscle  with  which  the  nerve 
is  connected,  or  if  a  sensory  nerve  the  centers  to  which  it 
goes,  but  in  a  very  slight  degree,  if  any,  the  fiber  itself.  If 
it  were  a  chemical  change  it  would  be  difficult  to  see  how 
an  exhaustion  caused  by  the  chemical  disintegration  could 
be  avoided.  The  only  explanation  left,  therefore,  seems  to 
be  that  it  is  some  kind  of  a  molecular  change  which  travels 
along  the  fiber,  a  molecular  change,  however,  of  the  nature 
of  which  we  are  still  wholly  at  sea. 

Several  things  about  the  impulse  are  known.  Its  rate 
of  speed  is  about  100  feet  per  second.  We  also  know  that 
the  nervous  impulse  is  in  the  nature  of  a  wave,  which  is 
about  18  millimeters  in  length.  This  is  a  little  over  seven- 
tenths  of  an  inch. 

The  wave-like  nature  of  the  impulse  is  evident  from, 
and  can  be  measured  by,  a  peculiar  electrical  wave  which 
runs  along  the  nerve  fiber  with  the  nervous  impulse,  which 
electrical  wave  is  easily  detected  by  means  of  the  galvano- 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM  445 

meter.  If  the  electrodes  of  a  sensitive  galvanometer  be 
placed  on  a  nerve  and  an  impulse  then  be  transmitted  along 
the  nerve  the  needle  of  the  galvanometer  will  be  deflected 
in  such  a  way  as  to  reveal  the  presence  of  a  current  at  the 
moment  the  nervous  impulse  is  passing.  This  current  has 
been  called  the  current  of  negative  variation.  This  wave 
of  variation  travels,  of  course,  with  the  same  speed  as  the 
impulse,  and  the  time  it  takes  to  pass  a  certain  point  can  be 
easily  determined.  One  has  simply  to  note  at  what  instant 
the  deflection  of  the  needle  begins  and  the  instant  it  ceases. 
Measurments  of  this  kind  have  shown  that  the  wave  takes 
only  about  .0007  of.  a  second  to  pass.  Thus,  knowing  its 
rate  of  speed  and  the  time  consumed  in  passing  a  given 
point,  it  is  a  simple  mathematical  calculation  to  show  that 
it  is  a  little  over  seven-tenths  of  an  inch  in  length.  The 
needle  further  indicates  that  at  first  this  current  is  very- 
feeble,  then  rises  to  a  maximum,  then  gradually  falls  and 
disappears. 

This  wave"  of  negative  variation  is  but  a  result  of  the 
nervous  impulse  and  is  caused  by  the  molecular  changes  in 
the  nerve  fiber  as  the  impulse  proceeds,  much  as  in  the 
running  of  a  train  there  might  be  along  the  rails  accom- 
panying the  train  currents  of  electricity  caused  by  the  fric- 
tion of  the  running  wheels,  which  current  might  be  easily 
detected  by  a  galvanometer  even  though  the  train  itself 
should  be  invisible. 

KINDS  OF  NERVE  FIBERS. 

Any  real  division  of  nerve  fibers  is  obviously  possible 
only  on  the  basis  of  the  organs  or  centers  with  which  they 
are  connected.  On  this  basis  nerve  fibers  are  divided  into 
two  classes,  the  first  called  the  afferent  or  sensory  fibers,  the 
second  the  efferent  or  motor  fibers.  The  terms  sensory  and 
motor  are,  however,  not  very  fortunate  ones,  as  there  are 
some  afferent  fibers  that  never  carry  sensations  which  reach 
consciousness,  while  many  of  the  motor  fibers  carry  impulses 
which  do  not  reach  muscles.  A  more  detailed  classification 
is  usually  made  as  follows: 


446  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

First. — Sensory  fibers  which,  when  stimulated,  produce 
sensations  of  which  we  are  conscious.  The  best  illustra- 
tions of  these  sensory  fibers  are  the  nerves  of  the  special 
senses. 

Second. — Reflex  sensory  fibers  which  when  excited  carry 
sensations  to  the  brain,  which,  however,  do  not  usually 
reach  consciousness,  but  in  the  lower  brain  centers  give  rise 
to  motor  impulses  without  the  intervention  of  the  will.  The 
best  illustration  of  these  possibly  is  the  narrowing  of  the 
pupil  when  subjected  to  a  strong  light.  Some  of  these  reflex 
sensory  fibers  may  occasionally  come  within  the  reach  of 
consciousness.  Many  of  them,  however,  are  entirely  outside 
of  it.  Such  are  the  reflex  sensory  fibers,  for  instance,  whicli 
carry  the  sensations  from  the  stomach,  when  food  reaches 
it,  to  the  brain,  to  be  there  translated  into  impulses  leading 
to  the  active  secretion  of  the  glands  of  the  stomach  or  to 
the  contraction  of  its  walls. 

Third. —  Inhibitory  sensory  fibers;  fibers  whicli  when 
stimulated  carry  sensations  to  nervous  centers  which  seem 
to  inhibit  their  action.  So,  for  instance,  the  biting  of  the 
lips  may  succeed  in  preventing  a  spasm  of  sneezing. 

The  three  classes  so  far  mentioned  are  included  iinder 
the  usual  term  of  sensory  fibers.  Of  the  efferent  nerve 
fibers  physiologists  usually  make  the  following  classes: 

Fourth.. — Motor  fibers  proper,  those  which  innervate  the 
muscles  and  produce  their  contractions.  Under  this  head 
are  included  not  only  the  nerves  which  run  to  the  skeletal 
muscles,  but  also  the  nerves  which  run  to  some  of  the  in- 
voluntary muscles,  especially  the  vaso-motor  fibers  which 
run  to  the  muscular  coats  of  the  blood-vessels. 

Fifth. — Secretory  fibers.  These  are  fibers  distributed  to 
the  cells  which  constitute  the  various  glands  of  the  body  and 
which  govern  their  secretion. 

Sixth. — Inhibitory  nerves  whicli  inhibit  muscular  action, 
the  clearest  example  of  which  is  the  inhibitory  nerve  of  the 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM.          447 

heart,  the  excitation  of  which  slows  the  rate  of  beat  in  this 
organ. 

All  the  nerves  so  far  mentioned  are  nerves  which  run  to 
the  periphery.  There  are,  of  course,  in  addition  to  these, 
many  nerves  which  never  get  beyond  the  central  nervous 
system,  but  which  run  in  this  for  their  entire  course  and 
serve  to  connect  the  various  centers  within  the  same,  car- 
rying between  these  centers  impulses  similar  to  those  car- 
ried by  peripheral  nerves. 

THE  GENERAL  PHYSIOLOGY  OF  NERVE  CENTERS. 

We  are  in  this  discussion  not  yet  concerned  with  the 
special  functions  of  the  various  nerve  centers,  but  merely 
with  those  phenomena  which  apply  more  or  less  fully  to  all 
nerve  cells.  In  this  general  way  nerve  cells  or  collections 
of  the  same  into  ganglia,  are  classed  as  follows: 

1. — Automatic  Centers.  These  are  centers  which  do  not 
seem  to  depend  on  some  specific  external  impulse  to  arouse 
them,  but  which  seem  to  act  more  or  less  independently  of 
all  such  stimuli.  The  best  illustration  is  possibly  that  of 
the  higher  centers  in  the  brain  which  we  are  wont  to  desig- 
nate as  the  centers  concerned  in  free  volition.  In  addition 
to  these  higher  psychic  centers  there  are  lower  automatic 
ones,  such,  for  instance,  as  the  automatic  centers  in  the 
heart  causing  the  beat  of  the  same  entirely  independently,  so 
far  as  we  know,  of  external  stimuli.  Such  automatic  cen- 
ters may,  of  course,  be  aroused,  and  within  certain  limits, 
controlled  by  outside  stimulation,  but  such  outside  stimula- 
tion need  not  be  the  invariable  occasion  for  their  acting. 

2. — Reflex  Centers.  These  are  centers  found  mainly  in 
the  spinal  cord,  but  present  also  in  the  brain,  to  which  sen- 
sory impulses  are  carried,  and  which  as  a  result  of  such  im- 
pulses originate  motor  impulses  in  harmony  with  these  sen- 
sations. When  working  normally  these  reflex  centers  are 
groups  of  cells  which  co-ordinate  the  incoming  impulses 
and  the  outgoing  impulses  to  produce  purposive  results. 
When  a  person  unknowingly  touches  a  hot  stove  with  his 


448  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

fingers  the  sensation  produced  by  the  burning  is  carried  to 
the  reflex  centers  in  the  spinal  cord  and  by  these  reflex 
centers  motor  impulses  are  sent  out  to  remove  the  hand. 
These  motor  impulses  are  in  harmony  with  the  incoming 
impulses  and  are  intended  for  specific  purposes. 

The  medulla  oblongata  contains  many  of  the  higher  re- 
flex centers.  Such,  for  instance,  as  the  reflex  centers  oc- 
casioning respiration;  the  reflex  center  controlling  the 
general  vascular  supply ;  the  reflex  center  regulating  the 
general  temperature  of  the  body,  and  others.  In  the  brain 
are  reflex  centers  co-ordinating  sensations  and  motions 
without  the  intervention  of  consciousness,  while  in  the 
spinal  cord  are  quite  a  number  of  centers  concerned  in  the 
manipulation  of  the  trunk  and  limbs. 

3. — Junction  Centers.  In  addition  to  the  automatic  cen- 
ters which  seem  to  have  the  power  to  originate  nervous 
impulses  and  the  reflex  centers  which  are  able  to  co-ordi- 
nate sensations  and  movements  without  appealing  to  con- 
sciousness there  are  a  number  of  ganglia,  the  function  of 
which  seems  to  be  entirely  that  of  a  relay  station  or  junction 
center.  For  instance,  the  spinal  root  ganglion  is  in  all  prob- 
ability nothing  more  than  a  relay  station  serving  merely  to 
act  as  a  center  of  nourishment  and  strength  to  the  nerve 
fiber  itself,  and  having  nothing  to  do  with  the  impulses 
traversing  it  save  to  make  more  possible  their  transmission. 
Much  as  in  a  system  of  telegraph  wires  there  are  relays  of 
batteries,  from  time  to  time,  concerned  only  in  making  the 
transmission  of  the  impulses  originated  in  other  ways  pos- 
sible. In  still  other  cases  nerve  centers  seem  to  be  mere 
junction  centers;  that  is,  centers  of  distribution.  A  single 
impulse  running  into  such  a  center  will  be  distributed 
through  the  many  cells  in  that  center  and  flow  out  of  it  in- 
creased many  fold.  The  ganglia  in  the  mesentery  and  ali- 
mentary canal  probably  serve  in  this  manner  and  make 
possible  that  the  few  impulses  reaching  these  organs  will  be 
finally  multiplied  and  distributed  as  to  reach  each  individual 
muscle  fiber  composing  them. 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.          449 

Having  now  treated  of  these  general  points  which  apply 
more  or  less  fully  to  nerve  cells  wherever  found,  the  ques- 
tion naturally  follows,  what  are  the  special  functions  of  the 
various  nerve  centers  found  in  the  body,  and  what  are 
the  specific  paths  of  the  fibers  connecting  these  centers 
with  each  other  and  with  the  periphery  ?  We  are  therefore 
concerned  next  with  the  finer  architecture  of  the  central 
nervous  system. 

THE  FINER  ARCHITECTURE  AND  THE  SPECIAL  PHYSIOLOGY 
OF  THE  CENTRAL  NERVOUS  SYSTEM. 

Perhaps  in  no  department  of  the  field  of  physiology 
have  the  views  been  so  materially  modified  of  late  as  in  the 
conceptions  of  the  structure  of  the  central  nervous  system. 
Recent  studies  of  such  men  as  Golgi,  Van  Gehuchten, 
Ramon  y  Cajal,  and  others  have  completely  changed  our 
notions  of  the  fundamental  structure  of  nervous  tissue.  It 
is  now  believed,  and  with  the  best  of  evidence,  that  the 
entire  nervous  system  is  made  up  of  separate  and  distinct 
units  called  neurons,  a  general  description  of  which  occurred 
in  the  preceding  pages. 

These  neurons  are  practically  all  alike,  at  least  ana- 
tomically, unless  we  except  those  of  the  cerebrum  to  which 
we  are  at  present  obliged  to  assign  psychic  functions.  No 
neuron  is  connected  with  any  other  neuron  directly,  but  the 
impulse  from  one  to  another  is  effected  at  the  point  where 
they  lie  either  close  together  or  in  possible  direct  contact. 
The  old  notion  of  a  continuous  network  of  nerve  fibers  per- 
vading the  entire  system  is  done  away  with. 

In  such  separate  and  distinct  neurons  the  cell  body  is 
the  physiological  and  nutritive  center.  To  this  center  im- 
pulses are  carried  by  some  of  its  branches,  and  from  it  in 
turn  impulses  are  carried  out  by  other  branches.  A  section 
of  any  of  the  branches  or  nerves  of  such  a  neuron  at  once 
results  in  the  death  of  that  end  of  the  nerve  severed  from 
the  cell  body.  It  is  the  purpose  in  this  paragraph  to  show 
in  an  elementary  way  but  with  some  special  detail  the  man- 
ner in  which  these  neurons  are  arranged  and  superposed. 
29 


450  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

1. — Arrangement  of  the  Motor  Neurons.  The  arrange- 
ment of  the  motor  neurons  is  about  as  follows:  In  the 
cortex  of  the  brain  near  the  fissure  of  Rolando  are  certain 
large  cells  which  give  off  small  branches  in  various  direc- 
tions and  usually  one  long  branch,  the  nerve  fiber  proper. 
This  extends  from  the  cortical  region  through  the  crus 
cerebri  of  its  side,  and  in  the  medulla  crosses  to  the  opposite 
side  of  the  cord.  It  then  descends  through  the  spinal  cord 
in  the  so-called  lateral  column  of  that  side,  commonly  des- 
ignated the  crossed  pyramidal  tract,  and  finally  enters  the 
anterior  horn  of  the  spinal  cord  and  ends  there  in  the  fine 
network  of  dendrons,  which  closely  invest  similar  short 
dendrons  of  the  motor  cells  of  the  anterior  horn.  These 
motor  cells  are  the  cell  bodies  of  the  second  neurons,  and 
their  nerve  fibers  extend  from  the  anterior  horn  through  the 
anterior  roots  of  the  spinal  nerve  to  the  muscles  in  ques- 
tion. In  other  words,  from  the  point  in  the  brain  where  the 
volition  arises  to  the  point  in  the  muscle  where  the  con- 
traction is  produced  there  are  two  neurons,  one  reaching 
from  the  brain,  where  the  cell  body  is,  through  the  cord  to 
the  anterior  horn,  the  second  neuron  reaching  from  this 
point  to  the  muscle.  This  is  the  usual  course  of  the  motor 
neurons. 

A  second  course  is,  however,  possible.  Many  motor 
fibers  arising  in  the  cortex  do  not  cross  to  the  opposite  side 
in  the  medulla,  but  descend  the  spinal  cord  on  the  same 
side  along  the  anterior  tracts,  and  then  along  in  the  course 
of  the  spinal  cord  cross  to  the  other  side,  through  the  an- 
terior commissure  of  the  cord.  It  will  be  seen,  however, 
that  all  these  motor  fibers  finally  reach  the  opposite  side  of 
the  cord,  and  the  difference  between  the  fibers  in  the 
lateral  column  and  those  in  the  direct  pyramidal  tract  is  a 
secondary  one.  The  fact  that  some  cross  in  the  medulla 
and  others  in  the  cord  further  down  is  no  real  difference. 
In  either  case  these  neurons  from  the  brain  end  in  the  an- 
terior gray  horns,  and  there  connect  with  the  second  motor 
neurons  which  reach  to  the  muscles.  The  general  arrange- 


(Facing  Page  450.) 

Fig.  144. — DIAGRAMMATIC  CROSS-SECTION  OF  THK  SPINAL  CORD  SHOWING  THE  MOTOR, 

RED,  AND  SENSORY,  BLUE,  PATHS.     (After  Van  Gehuchten.) 

1,  crossed  or  lateral  pyramidal  tract;  2,  direct,  or  anterior  pyramidal  tract;  3,  posterior 
sensory  columns ;  4,  direct  cerebellar  tract ;  5,  antero-lateral  ground  bundles ;  6,  crossed 
sensory,  or  antero-lateral  ascending  tract. 


(Facing  Page  450.) 

Fig.  142.— DIAGRAM  OF  THE  MOTOR  PATHS  SHOWING  THEIR  MANNER  OF  CROSSING  EITHER 
IN  THE  PYRAMIDS  OR  LOWER  IN  THE  CORD.     (After  Van  Gehuchten.) 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         451 


ment  of  this  is  schematically  indicated  in  the  accompanying 
diagram,  in  which  the  reader  will  find  it  possible  to  follow 
the  description  of  the  text. 

2 . — The  A  rrangement  of  the 
Sensory  Neurons.  The  sensory 
neurons  are  more  complicated, 
but  in  a  general  way  here,  too, 
there  are  two  neurons  reaching 
from  the  sense-organ  to  the 
brain.  The  first  neuron  has  its 
cell  body  in  the  spinal  root 
ganglion.  From  this  body  one 
nerve  goes  to  the  touch  corpus- 
cles, say  of  the  finger,  while 
from  the  same  body  a  second 
nerve  fiber  runs  into  the  poste- 
rior horn  of  the  spinal  cord. 
To  repeat :  One  neuron  bridges 
the  distance  from  the  point  of 
touch  in  the  finger  to  the  spinal 


COrd  with  the  Cell    body  of    this    Fig-  143— DIAGRAM  TO  SHOW  PATHS  OF 

NERVE-FIBERS  IN  THE  SPINAL  CORD. 

(After  v.  Lenhossek.) 


neuron    located    in    the   spinal 
root  ganglion.     The  endings  of 


M,   voluntary    muscle;     If,    skin    of 


.,   .  -.,  •         ,,  1  1     hand;  T,  touch  corpuscle;  HW,  posterior 

this  sensory  fiber   m   the   cord  root  spinal  nerve.   VWt  anterior  root 
are  in  a  general  way  as  follows:    spinal  nerve;  pp>  sensory  nerve'-  #»• 

spinal  root  ganglion;  s,  cell  body  of  sen- 
As  SOOn   aS  the  fiber  reaches    sory  neuron;   m,  motor  cells  in  anterior 


the  posterior  horn  it  divides  in- 

to  an  ascending  and  a  descend-  &lion;  «.  6«  a  continuation  of  sensory 

.  neuron    c,   upwards  and    downwards 

ing    branch  Which    paSS    Up   and    through  gray  matter  of  posterior  horn; 

down  respectively  through  the  *•  *  ne"rKon  lying  entirely  within  the 

cord,  and  by  means  of  the  collaterals  a  a, 
gray     matter     of      the      posterior    connecting  opposite  sides  of  the  cord. 

horn.       From    these    branches  ^%SX£S 

smaller  branches  called  collat-   Paths  there  described. 
erals   are   given  off  at  right  angles.     Some  of  these  main 
branches  or  collaterals  may  run  into  the  anterior  horns,  and 
there  end  in  capillary  dendrons  which  invest  the  motor  cells 


452  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

found  here.  It  is  this  arrangement  af  the  neurons  of  sensa- 
tion and  motion  which  makes  the  simple  reflex  actions  of 
the  cord  possible. 

Other  branches  or  collaterals  with  their  dendrons  invest 
cells  found  in  Clark's  column.  These  cells  in  Clark's 
column  are  the  beginnings  of  new  neurons  which  reach 
from  Clark's  column  in  the  spinal  cord  to  the  cerebellum, 
the  fibers  ascending  in  the  direct  cerebellar  tract.  In  this 
way  sensations  are  carried  to  the  motor  cells  of  the  cerebel- 
lum and  make  the  reflex  actions  of  the  cerebellum  possible. 

None  of  the  two  paths  just  mentioned,  however,  result 
in  conscious  sensation.  There  is  a  third  path  which  leads 
to  the  cerebrum  itself.  This  path  is  about  as  follows:  The 
sensory  nerves  or  branches  from  them,  leave  the  posterior 
horn  of  the  spinal  cord  and  ascend  towards  the  brain  through 
the  posterior  columns.  Many  of  these  fibers  run  as  far  as 
the  medulla.  In  the  gray  matter  of  the  medulla,  however, 
their  dendrons  invest  new  cells,  nerves  from  which,  after 
crossing  in  the  medulla,  extend  to  the  cortex  of  the  brain. 

While  most  of  the  sensory  fibers  running  up  the  pos- 
terior column  connect  with  their  second  neuron  in  the  me- 
dulla, many  of  them  run  into  the  gray  matter  of  the  spinal 
cord  before  reaching  the  medulla,  and  there  invest  cells  the 
nerves  from  which  then  cross  to  the  opposite  side  of  the 
spinal  cord  and  reach  the  cortex  of  the  brain.  The  path  for 
these  crossed  sensory  fibers  of  the  cord  is  the  antero-lateral- 
ascending  tract. 

An  additional  sensory  path  needs  mentioning.  Some  of 
the  branches  or  collaterals  of  the  sensory  fibers  may  con- 
nect with  neurons  in  the  gray  matter  of  the  cord,  which  run 
to  the  opposite  side  of  the  cord  and  connect  with  other 
neurons  there.  That  such  paths  exist  is  proved  by  the  fact 
that  when  the  sensory  fibers  of  one  side  of  the  spinal  cord 
are  cut  sensation  is  not  lost,  but  seems  actually  for  a  little 
while  to  be  increased.  This  can,  of  course,  only  be  ex- 
plained by  assuming  that  fibers  must  connect  with  the  oppo- 
site or  uninjured  side  of  the  cord. 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM.          453 

With  the  motor  impulses  the  case  is  different.  When 
the  motor  fibers  of  one  side  are  cut  that  side  is  completely 
paralyzed,  even  when  the  other  side  is  left  intact,  showing 
that  the  motor  paths  are  direct. 

3. — Summary  of  Nerve  Paths.  To  summarize,  then, 
there  are  the  following  sensory  paths : 

First.  The  neuron  extending  from  the  finger  to  the 
spinal  root  ganglion  and  from  there  in  turn  to  the  posterior 
horn  of  the  spinal  cord,  may  run  directly  to  the  anterior 
horn  and  invest  with  its  dendrons  a  motor  cell  there,  and 
so  produce  the  path  for  the  simple  spinal  cord  reflexes. 

Second.  The  first  sensory  neuron  may  run  not  to  the 
motor  cells,  but  to  the  cells  forming  Clark's  column  and  in- 
vest one  of  these  with  its  dendron,  which  cell  in  turn  as  a 
new  neuron  extends  to  the  cerebellum  and  makes  possible 
the  cerebellar  reflexes. 

Third.  The  first  neuron  or  branches  of  it  may  connect 
with  a  neuron  of  the  spinal  cord  which  runs  to  the  opposite 
side  of  the  spinal  cord  and  there  connects  with  other 
neurons.  This  path  makes  possible  the  radiation  of  sensa- 
tions to  both  sides  of  the  spinal  cord. 

Foitrth.  The  first  neuron  may  connect  with  neurons 
running  to  the  cerebrum  (a)  by  running  up  through  the 
posterior  columns  and  connecting  with  the  second  neuron 
in  the  medulla,  which  neuron  there  crosses  and  goes  to  the 
opposite  cerebral  hemisphere;  or  (b)  the  first  neuron  after 
ascending  a  short  distance  through  the  posterior  column 
enters  the  gray  matter  of  the  cord  and  there  connects  with  a 
neuron  which  crosses  to  the  opposite  side  of  the  cord,  and 
in  the  antero-lateral  tract  reaches  the  cerebral  hemispheres 
the  same  as  the  neurons  which  cross  in  the  medulla. 

4. — Where  Do  the  Sensory  Neurons  End  in  the  Brain? 
A  very  interesting  question  now  arises,  with  what  do  these 
sensory  neurons  connect  in  the  cortex  of  the  brain?  While 
this  is  possibly  still  debatable  ground,  it  seems  very  proba- 


454 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


ble  that  these  sensory  neurons  with  their  capillary  dendrons 
at  their  ends  invest  the  motor  cells  which  form  the  first 
neurons  of  the  motor  path.  If  this  be  true,  it  gives  to  these 
cells  the  wonderful  faculty  of  not  only  serving  as  voluntary 
motor  cells,  but  as  conscious  sensory  cells.  In  other  words, 
in  these  cortical  cells  the  consciousness  of  sensation  as  well 
'*  as  the  consciousness  of  volition  is  located. 

5. — Comparison  of  Sensory  and  Motor  Paths.  It  will 
be  noticed  that  in  the  sensory,  as  in  the  motor  path,  there 
are  essentially  two  neurons  between  the  periphery  and  the 
brain.  Further,  both  sensory  and  motor  neurons  cross,  either 
in  the  medulla,  or  further  down  in  the  cord.  An  interesting 
difference  between  the  sensory  and  motor  neurons  lies  in  the 
fact  that  in  one  case  the  cell  body  of  the  lower  neuron  lies 


Fig.  145. — DIAGRAM  SHOWING  THE  PATHS  OF  FIBERS  IN  THE  CEREBRO-SPINAL  SYSTEM. 

Outgoing  arrows  indicate  motor,  incoming  arrows  sensory  fibers. 

JK,  R,  right  and  left  cerebral  hemispheres;  G,  G,  gray  matter  of  mid-brain,  optic  thai- 
ami  and  upper  medulla;  H,  H,  lower  portion  of  medulla  where  the  cranial  nerves  take 
their  origin;  H,H  (at  bottom  of  figure),  the  gray  matter  of  spinal  cord;  la,  motor  nerves; 
Ib,  sensory  nerves;  6,  G,  fibers  connecting  the  hemispheres;  Ic,  half-crossed  optic  fibers; 
5,5,  fibers  connecting  different  portions  of  same  hemisphere;  2,2,  crossed  pyramidal 
tract;  2',  2',  direct  pyramidal  tract  crossing  in  the  cord;  #,  3,  sensory  fibers,  some  cross- 
ing in  the  pyramids  (others  have  crossed  in  the  cord,  not  shown),  but  all  passing  through 
the  gray  matter  G.  By  reference  to  the  text  the  diagram  will  be  more  intelligible. 

outside  of  the  spinal  cord,  in  the  spinal  root  ganglion,  while 
in  the  case  of  the  motor  neurons  it  lies  inside  of  the  spinal 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         455 

cord,  in  the  gray  matter  of  the  anterior  horns.  This  differ- 
ence of  position  is,  of  course,  physiologically  a  secondary 
one. 

The  sensory  cranial  nerves  find  their  counterparts  of  the 
spinal  root  ganglia  in  the  sensory  ganglia  which  they  pos- 
sess. Such,  for  instance,  as  the  Gasserian  ganglion  of  the 
fifth  cranial  nerve. 

It  simplifies  the  conception  of  the  sympathetic  system, 
to  look  upon  the  sympathetic  ganglia  lying  along  the  spinal 
cord  as  a  second  set  of  spinal  root  ganglia  containing  sen- 
sory and  possibly  motor  neurons,  which  in  this  case  reach 
from  the  spinal  cord  to  the  viscera,  instead  of  to  the  body 
wall  and  skin  as  in  the  case  of  the  spinal  root  ganglia  proper. 
This  conception  of  the  sympathetic  ganglia  as  spinal  root 
ganglia  lends  a  unity  to  the  entire  nervous  system,  doing 
away  at  once  with  the  too  general  notion  that  the  sympa- 
thetic system  is  a  special  system  only  incidentally  connected 
with  the  spinal  cord. 

THE  MEDULLA. 

In  the  medulla  the  general  arrangement  of  gray  and 
white  matter  found  in  the  cord  is  materially  varied  from  for 
several  reasons.  In  the  first  place,  the  decussation  of  the 
motor  and  sensory  fibers  displaces  the  gray  matter.  In 
addition  to  that  we  find  here  many  new  centers.  In  the 
medulla  are  located,  for  instance,  the  center  governing 
respiration,  that  governing  the  temperature  of  the  body, 
that  governing  the  vascular  supply,  and  others.  In  addi- 
tion to  that  we  find  here  much  gray  matter,  the  cells  of 
which  are  probably  the  second  neurons  of  sensation  just 
described.  Here,  also,  are  a  number  of  centers  connected 
with  the  nerves  of  the  special  senses.  The  exact  location 
of  these  centers  is  omitted  from  this  elementary  discussion 
as  being  too  complicated.  There  remains,  therefore,  for 
further  description  the  arrangement  of  fibers  and  centers  in 
the  cerebellum  and  cerebrum. 


456  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

SPECIAL  FUNCTIONS  OF  THE  BRAIN  AND  COED. 

It  was  pointed  out  that  the  function  of  the  spinal  cord  is 
two-fold.  First,  it  serves  as  a  tract  along  which  sensory  and 
motor  fibers  run  that  connect  the  brain  with  the  distant  por- 
tions of  the  body.  Second,  it  consists  of  centers  which  are 
concerned  in  the  simple  reflex  actions.  Thus,  if  a  frog  be 
taken  and  its  brain  removed,  and  the  toe  of  such  a  frog 
pinched,  the  leg  will  be  drawn  up  with  almost  as  much 
precision  as  in  the  case  of  an  uninjured  frog.  A  piece  of 
blotting  paper  soaked  with  an  irritating  solution,  such  as  an 
acid,  placed  on  his  skin  will  produce  a  series  of  the  most 
perfectly  co-ordinated  movements.  If  the  foot  be  held  firmly 
and  then  pinched  the  frog  at  first  tries  to  pull  away  the 
injured  foot  and  upon  repeated  failures  to  accomplish  this  it 
will  bring  into  play  the  foot  on  the  other  side  to  effect  his 
purpose.  Here  is  a  case  in  which  the  reflexes  have  become 
complicated,  have  called  in  the  opposite  side  of  the  spinal 
cord,  and  yet  are  all  so  co-ordinated  as  to  be  directly  pur- 
posive. 

The  question  whether  there  are  any  automatic  centers 
in  the  spinal  cord  is  still  an  open  one,  but  the  evidence 
seems  to  show  that  it  possesses  reflex  centers  only.  Instances 
of  impulses  which  seem  to  have  originated  in  the  spinal 
cord  have  generally  been  traceable  to  outside  influences  for 
their  occasion.  These  outside  influences  are  of  course  two. 
First,  sensations,  carried  by  the  sensory  neurons  directly  to 
it.  In  this  case  a  reflex  action  arises  without  the  interven- 
tion of  the  brain.  Second,  motor  impulses  from  the  higher 
centers  of  the  brain.  These  higher  impulses  from  the  brain 
calling  into  action  these  motor  centers  produce  the  ordinary 
voluntary  movements  as  we  know  them. 

While  most  of  the  reflexes  of  the  spinal  cord  are  natural, 
that  is,  inherited,  it  is  possible  by  training  to  establish 
reflexes  of  a  highly  acquired  character.  Much  of  the  quick 
perception  and  delicate  touch  of  an  artist  on  most  any  kind 
of  an  instrument  is  due  to  the  establishment  of  fine  reflexes 
in  his  spinal  cord.  Such  an  artist  is  frequently  able  to  re- 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.          457 

act  to  his  sensations  without  the  direct  intervention  of  his 
brain. 

SPECIAL  PHYSIOLOGY  OF  THE  MEDULLA. 

In  the  medulla,  too,  we  find  reflex  centers,  but  the  reflex 
centers  are  here  of  a  higher  kind.  They  are  still  involuntary 
and  largely  outside  of  the  control  of  the  will,  but  are  not  the 
simple  muscular  reflexes  of  the  cord.  They  are  the  higher 
reflexes  governing  complicated  systems  in  the  body.  In 
fact,  it  may  be  proper  to  speak  of  the  reflexes  here  as  the 
systemic  reflexes.  Instances  of  the  reflex  centers  of  breath- 
ing, circulation  and  temperature  have  already  been  noted. 
In  addition  to  these  we  find  in  the  medulla  some  of  the 
simpler  reflexes,  the  sensation  occasioning  which  are  derived 
from  the  special  senses. 

THE  PHYSIOLOGY  OF  THE  CEREBELLUM. 

It  is  exceedingly  difficult  to  determine  definitely  the  func- 
tions of  such  complicated  structures  as  the  cerebrum  and 
the  cerebellum.  The  structures  are  so  delicate  and  the 
methods  of  operation  upon  them  to  determine  their  func- 
tions so  coarse  that  it  is  frequently  difficult  to  argue  from 
cause  to  effect.  One  can  easily  imagine  how  much  progress 
would  be  made  by  an  individual  trying  to  understand  the 
workings  of  a  watch  by  standing  off  at  a  distance  and  firing 
pistol  shots  at  it  and  then  noting  the  result ;  firing  first  at  the 
hand,  then  the  face  of  the  watch,  then  spring  or  case.  One 
can  easily  see  the  almost  utter  hopelessness  of  ever  getting 
at  a  complete  knowledge  of  a  watch  by  such  rude  means, 
and  yet  incisions  or  stimulations,  in  fact  all  of  the  experi- 
ments made  on  the  brains  of  animals  have  been  relatively 
as  rough  and  inexact  as  the  firing  of  a  pistol  into  the  deli- 
cate watch.  A  few  general  points  are,  however,  available. 

It  seems  probable  that  the  function  of  the  cerebellum  is 
that  of  a  large  motor  center  to  whose  jurisdiction  are  con- 
signed the  ordinary  habitual  motions  of  the  body ;  walking, 
running,  in  case  of  animals,  flying  or  swimming.  These 
motor  habits  are  doubtless  acquired  painfully  and  slowly 


458 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


by  the  cerebrum,  as  for  instance,  in  the  case  of  an  infant 
learning  to  walk  or  crawl.  As  they  are  repeated  over  and 
over  again  they  become  more  and  more  habitual.  They 
seem  to  be  delegated  more  and  more  by  the  conscious  cere- 
brum to  the  lower  cerebel- 
lum, and  in  this  way  the 
activity  of  the  cerebrum 
left  to  higher  functions  in- 
stead of  continually  wast- 
ing its  strength  in  looking 
after  the  contraction  of 
the  muscles  in  moving  the 
body. 

If,  for  instance,  the  cere- 
bellum be  removed  from 
the  brain  of  a  pigeon  the 
animal  sits  quietly,  seems 
to  be  conscious  of  dan- 
ger; seems,  in  short,  to 
retain  most  of  its  psychic 
functions,  but  is  awkward 
in  its  walk,  stumbles  and 
falls  easily,  and  flies  with 
the  greatest  difficulty.  It 
has  lost  control,  apparent- 
ly, of  the  motions  which 
originally  it  performed 
with  rapidity  and  precis- 
ion. Removals  of  the  cere- 
bellum from  other  animals 
have  in  a  general  way 
shown  similar  results. 

Without  going  into  fur- 
ther detail  the  whole  point 
may  be  summed  up  in  the  statement  that  it  is  the  governing 
center  for  the  general  habitual  motions  of  the  body.  The 
physiological  value  of  this  is  at  once  clear  when  we  remem- 


Fig.  146. —SECTION  OF  THE  CORTEX  OF  CERE- 
BELLUM.   (After  Sankey.) 
a,  pia-mater  with  contained  blood-vessels; 
&,  external  layer  of  gray  matter;  c,  layer  of  cor- 
puscles (nerve  cells)  of  Purkinje;  d,  inner  gran- 
ule layer;  e,  medulla. 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM.          459 

her  that  by  delegating  the  control  over  these  complicated 
motions  to  the  cerebellum  the  cerebrum  is  enabled  to  turn 
its  attention  to  higher  functions. 

THE  PHYSIOLOGY  OF  THE  MID -BRAIN. 

In  giving  the  functions  of  the  mid-brain  it  is  desirable 
to  include  the  optic  thalami,  for  although  these  bodies  are 
anatomically  classed  with  the  cerebrum  they  belong  physi- 
ologically to  the  mid-brain.  The  crura  cerebri  of  the  mid- 
brain  are,  of  course,  mere  bands  of  fibers  connecting  spinal 
cord  and  brain,  so  that  we  have  to  do  here  only  with  the 
corpora  quadrigemina  of  the  dorsal  side. 

The  difficulty  of  experimenting  on  these  structures, 
since  they  are  hard  to  reach  without  injuring  other  parts  of 
the  brain,  makes  our  knowledge  somewhat  fragmentary. 
Enough  evidence  is,  however,  at  hand  to  show  that  the 
corpora  quadrigemina,  especially,  are  great  reflex  centers 
between  visual  impressions  and  the  motor  impulses  which 
govern  the  movements  of  the  eyeballs.  Here,  without  the 
intervention  of  consciousness,  the  visual  sensations  produce 
reflexes,  by  means  of  which  the  eyeballs  are  turned  as  oc- 
casion or  necessity  requires.  Every  one  is  aware  that  he 
keeps  his  eyeballs  in  constant  motion  turning  hither  and 
thither  as  one  object  after  another  arrests  his  attention,  and 
yet  does  all  of  this  without  any  real  conscious  intervention. 
It  is  only  when  special  points  come  up  demanding  special 
scrutiny  that  we  become  consciously  aware  and  in  a  volun- 
tary way  direct  the  muscular  movements  of  the  eye.  That 
visual  sensations  figure  so  prominently  in  all  our  actions, 
shows  the  necessity,  or  at  least  the  great  desirability,  of 
having  a  reflex  center  where  these  many  visual  sensations 
may  be  properly  interpreted  and  reflected  in  purposeful 
motor  impulses. 

But  not  only  do  the  motor  impulses  of  the  eye  originate 
here  but  the  optic  thalami  and  mid-brain  seem  also  to  be 
materially  concerned  in  receiving  the  visual  sensations  and 
reflecting  them  in  purposeful  locomotary  impulses.  It  is 


460  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

an  every-day  experience  that  one  will  go  along  a  path  step- 
ping over  all  obstacles,  walking  around  obstructions,  getting 
out  of  the  way  of  passers-by  or  vehicles,  stepping  carefully 
sometimes  over  pools  of  water,  even  ascending  steps,  and 
yet  do  all  of  this  without  the  slightest  apparent  intervention 
of  consciousness.  During  all  of  this  time  a  person  may  be 
deeply  absorbed  in  some  train  of  thought,  and  if  he  were 
questioned  at  the  end  of  his  journey  about  any  of  the  de- 
tails of  the  way  would  be  utterly  unable  to  recall  even  a 
few.  It  is  of  course  also  evident  that  nearly  all  of  the 
motions  of  the  body  are  guided  by  the  sensations  of  sight. 
True  an  individual  may  walk  or  run  with  his  eyes  shut  and 
depend  upon  other  sensations,  but  that  is  only  possible 
where  the  individual  knows  the  road  to  begin  with,  or  is 
supremely  indifferent  to  accidents.  Ordinarily  speaking, 
the  visual  impressions  which  never  reach  consciousness  are 
the  guides  which  determine  the  motions  of  the  body.  These 
complicated  reflexes  have  their  seat  in  the  optic  thalami  or 
mid-brain,  and  for  the  final  execution  of  some  of  the  habitual 
movements  of  the  body  the  cerebellum  also  comes  into  play. 
It  needs  no  special  comment  to  point  out  what  a  saving  of 
energy  it  is  to  the  higher  centers  of  the  brain  to  be  relieved 
from  the  interpretation  of  the  crowd  of  sensations  pouring 
in  through  eye  (or  ear)  and  their  proper  reflection  into  cor- 
respondingly purposeful  motor  impulses. 

It  will  be  pointed  out  later  that  the  place  where  visual 
sensations  come  into  the  field  of  consciousness  lies  in  the 
occipital  lobes  of  the  brain.  Here  seems  to  be  the  curtain 
of  the  mind  against  which  the  images  are  projected  for 
direct  and  conscious  scrutiny.  But  a  small  proportion, 
however,  of  the  visual  sensations  reach  this  high  conscious 
center.  Most  of  them  never  get  beyond  the  sub-conscious 
and  reflex  centers  of  optic  thalami  and  mid-brain.  An 
animal  whose  occipital  lobes  are  removed,  and  which  is 
therefore  consciously  blind,  is  still  able  to  avoid  obstacles 
in  its  way  and  prevent  itself  from  stumbling  over  obstruc- 
tions by  going  around  them,  on  account  of  the  fact  that  the 


ANATOMY,   PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         461 

sub-conscious  reflexes  referred  to  are  still  intact.  Such  a 
dog,  however,  makes  no  difference  between  an  obstacle,  as 
a  dish  of  food,  or  a  dangerous  or  threatening  obstruction. 
He  is  able  to  make  no  conscious  interpretation,  and  by  his 
sub-conscious  centers  both  the  inviting  food  before  him  or 
the  threatening  rod  are  mere  obstacles  to  be  avoided  lest  he 
should  run  against  them. 

Leaving  now  all  of  these  lower  centers  of  the  nervous 
system  we  reach  finally  the  cerebrum  itself,  where,  as  far 
as  we  know,  the  nerve  centers  have  associated  with  them 
for  the  first  time  that  peculiar  property  which  we  are  wont 
to  designate  as  consciousness. 

THE  PHYSIOLOGY  OF  THE  BRAIN  AND  THE  LOCALIZATION 
OF  CENTERS. 

The  careful  work  of  such  men  as  Jackson,  Hitzig, 
Fritsch,  Beevor,  Horseley  and  Ferrier  has  enabled  us  to 
mark  off  the  physiological  topography  of  the  cortex  of  the 
brain  and  to  establish  for  definite  portions  of  the  cortex 
certain  specific  and  definite  functions.  Their  researches 
have  completely  disproved  the  older  notion  that  the  entire 
brain  acted  as  a  unit  in  every  brain  act;  that  a  sensation,  or 
a  volition,  or  a  memory  were  actions  participated  in  by  the 
entire  brain  as  one  structure.  We  now  know  that  memory 
is  no  such  a  simple  thing,  but  that  in  certain  portions  of 
the  brain  are  stored  auditory  sensations,  in  other  visual 
sensations,  and  so  on.  We  know  that  in  certain  portions  of 
the  brain  the  voluntary  impulses  arise  that  move  the  foot ; 
in  other  definite  regions  those  that  govern  the  movements  of 
the  hand.  It  has  even  been  possible  by  pathological  ob- 
servations to  establish  the  position  of  the  center  of  speech. 
The  topography  of  the  brain  as  given  in  the  accompanying 
diagram  is  that  now  generally  accepted. 

The  position  of  these  centers  has  been  determined  ex- 
perimentally in  one  or  more  of  the  following  ways : 

First.     It  not  infrequently  happens  that  persons  are  born 
possessing  certain  brain  malformations.    By  the  post  mortem 
30 


462  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

determination  of  these  anatomical  malformations  and  their 
comparison  with  the  observed  mental  acts,  deductions  have 
been  arrived  at  as  to  the  function  of  the  parts  affected. 

Second.  Occasionally  a  normal  brain  is  pathologically 
injured  either  by  compression,  as  in  accidents,  by  inflam- 
mation in  disease,  or  by  the  formation  of  tumors  in  certain 
portions  of  its  structure.  It  was  by  noticing  the  fact  that 
the  presence  of  a  tumor  in  the  left  frontal  lobe  of  the  brain 
was  always  associated  with  the  loss  of  speech  that  that  cen- 
ter was  finally  localized  in  that  region. 

Third.  Upon  animals  it  has  been  possible  to  cut  off 
certain  regions  of  the  brain  to  note  the  physiological  effects  of 
such  excisions.  It  was,  for  instance,  by  the  extirpation  of 
the  occipital  lobes  of  the  brain  that  the  center  of  conscious 
vision  was  definitely  located. 

Fourth.  By  stimulation  experiments  made  directly  on 
the  cortex  of  the  brain.  A  new  era  in  brain  physiology  was 
ushered  in  when  Fritsch,  Hitzig,  and  later  Ferrier,  suc- 
ceeded in  producing  movements  by  electrically  stimulating 
certain  regions  of  the  cortex  of  the  brain.  By  subjecting 
various  portions  of  the  cortex  to  such  stimuli  and  noting 
what  muscles  of  the  body  were  affected  by  the  motor  im- 
pulses so  originated,  it  was  soon  relatively  easy  to  map  out 
the  motor  topography  of  the  cortex,  and  it  is  upon  these  ex- 
periments that  the  results  in  the  diagram  are  based. 

Fifth.  For  the  determination  not  only  of  the  centers  of 
the  brain,  but  of  the  nerve  fibers  which  extend  from  them, 
two  methods  of  study  suggested  themselves,  (a)  In  the 
embryonic  development  of  animals  it  was  found  that  certain 
cells  and  certain  nerve  fibers  developed  sooner  than  others, 
so  that  in  this  way  it  was  possible  to  give  the  region  and 
follow  the  course  of  certain  nerve  fibers  before  neighboring 
ones  with  which  they  might  later  be  confused  had  de- 
veloped, (b)  A  method  productive  of  even  more  results 
than  this  was  what  was  called  the  Wallerian  method,  or  the 
method  of  degeneration.  It  has  already  been  pointed  out. 


-8 


A3 


VTSU' 

(Facing  Page  463.) 

Fig.  147.— DIAGRAM  OF  THE  VISUAL  PATHS.  (Modified  from  Vialet.) 
OP.  N,  optic  nerve;  OP.  C,  optic  commissure;  OP.  T,  optic  tract;  OP.  R,  optic  radia- 
tions; V.  S,  visual  speech  center;  A.  S,  auditory  speech  center;  M.  S,  motor  speech  cen- 
ter. A  lesion  or  section  at  1  causes  blindness  of  that  eye;  at  2,  blindness  of  the  outer  half 
of  each  eye ;  at  3,  blindness  of  the  nasal  half  of  that  eye ;  similar  lesions  at  3  and  3',  blind- 
ness of  nasal  halves  of  both  retinas;  at  4,  blindness  of  nasal  half  of  one  eye  and  temporal 
half  of  opposite  eye;  at  8,  on  left  side,  word  blindness 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM. 


463 


that  when  the  cell  bodies  to  which  nerves  are  attached  are 
destroyed  in  any  way,  these  nerves  at  once  die  to  their  per- 
iphery. By  this  method  it  was  possible  to  destroy  certain 
brain  centers  and  thus  destroy  the  entire  bundle  of  nerves 
leading  out  from  it.  This,  o"f  course,  enabled  the  observer 
to  determine  over  what  part  of  the  body  the  nerve  centers 
in  question  had  jurisdiction.  It  was  this  method  of  degen- 
eration that  helped  materially  in  giving  us  our  knowledge 
as  we  now  have  it  of  the  courses  of  the  fibers  in  the  spinal 
cord. 

THE  PHYSIOLOGICAL  TOPOGRAPHY  OF  THE  BRAIN. 

1. — The  Motor  Areas.  The  motor  areas  of  the  brain  lie 
along  the  fissure  of  Rolando.  At  the  top  of  this  fissure  are 
the  motor  areas  governing  the  toes.  These  are  followed  by 
motor  nerves  which  govern  regions  gradually  higher  up, 
until  at  the  bottom  of  the  fissure  of  Rolando  we  come  to 
those  motor  areas  concerned  in  the  control  of  lips,  larynx 
and  mouth.  The  proximity  of  these  motor  centers  to  the 
speech  center  on  the  left  side  is  worth  noting. 

2. — The  Seat  of  Conscious  Tactile  Sensations.  But  not 
only  are  these  motor  centers  concerned  in  the  production  of 
the  voluntary  impulses.  They  are  also  the  seat  of  the  sen- 
sations which  arise  in  the  portions,  the  motions  of  which 
they  control.  Thus  the  motor  area  along  the  fissure  of  Ro- 
lando governing  the  muscles  of  the  finger  is  probably  also 
the  center  in  which  the  sensory  impulses  coming  from  the 
finger  are  finally  interpreted  as  conscious  sensations.  This 
area  ought,  therefore,  more  properly  to  be  called  the  motor- 
sensory  area. 

3. — The  Visual  Center.  In  the  occipital  lobes  the  visual 
center  is  located.  It  is  of  interest  to  point  out  here  that 
while  for  the  motor  areas  the  right  side  of  the  brain  gov- 
erns the  left  side  of  the  body,  and  vice  versa,  there  is  not 
such  a  complete  crossing  for  the  optic  nerves.  There  is,  in 
fact,  in  the  optic  nerve  only  a  half  crossing.  In  the  right 


464  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

occipital  lobe  arise  the  fibers  for  the  left  half  of  each  retina, 
while  from  the  left  occipital  lobe  the  right  half  of  each  re- 
tina is  innervated.  This  half  decussation,  of  course,  occurs 
in  the  optic  commissure.  The  destruction  of  one  of  the 
occipital  lobes,  therefore,  produces  blindness  in  the  oppo- 
site half  of  each  eye. 

4. — The  Auditory  Center.  Immediately  below  the  fis- 
sure of  Sylvius,  in  the  upper  convolution  of  each  temporal 
lobe  is  located  the  center  of  hearing.  Here  are  stored 
away  the  memories  of  the  meanings  of  all  heard  words  and 
sounds.  Some  investigators  give  the  center  for  perception 
of  musical  sounds  as  somewhat  forward  from  the  place  where 
ordinary  sounded  words  are  stored. 

5. — The  Centers  for  Taste,  Smell  and  Speech.  Below 
the  auditory  centers  in  the  temporal  lobes  seem  to  be  located 
the  centers  for  taste  and  smell.  One  of  the  most  interest- 
ing of  all  of  the  centers,  and  strange,  too,  one  of  the  first 
to  be  localized,  is  the  center  of  speech.  This  lies  in  the 
left  frontal  lobe  immediately  anterior  to  the  motor  areas 
governing  lips,  pharynx  and  mouth.  The  fact  that  this 
center  is  usually  located  on  the  left  side  is  explained  by  the 
circumstance  probably  that  most  persons  write  with  their 
right-hand,  which  is  a  'form  of  speaking  as  far  as  the  intel- 
lectual part  of  it  is  concerned.  Persons  who  have  habitu- 
ally written  with  their  left-hands  would  be  more  liable  to 
have  the  center  of  speech  located  on  the  right  side.  The 
interesting  question  arises,  why  such  a  center  should  be  on 
the  one  side  only?  There  is  no  satisfactory  reason  for  this, 
unless  it  be  that  as  speech  is  such  a  unit,  and  as  its  coher- 
ency would  require  such  a  careful  co-ordination  of  two  sides, 
it  would  hardly  be  probable  that  such  could  be  accomplished 
from  the  action  of  two  separate  centers.  .There  is  the  possi- 
bility of  directing  the  two  eyes  to  two  different  objects,  as 
in  the  case  of  cross-eyed  persons,  and  the  ability  thus  to 
see,  to  some  extent  at  least,  double.  Similar  double  sen- 
sations are  possible  with  the  ear.  Double  motions  from  the 


ANATOMY,  PHYSIOLOGY,  OF  NERVOUS  SYSTEM.         465 

right  and  left  side  are  perfectly  natural,  but  it  can  be  easily 
seen  that  coherent  speech  is  a  unity  which  could  not  easily 
result  from  the  actions  of  two  separate  sources  or  agencies. 

CONSCIOUSNESS. 

The  question  is  repeatedly  asked  in  what  sense  conscious- 
ness is  a  physiological  property.  This  whole  point  may 
be  dismissed  as  far  as  its  physiology  is  concerned  by  the 
statement  that  of  its  real  nature  we  know  scientifically  ab- 
solutely nothing.  Held  by  some  to  be  merely  a  high  form 
of  mechanical  or  chemical  changes  in  certain  cells,  the 
phenomena  of  consciousness  have  been  reduced  to  merely 
physical  phenomena  and  so  robbed  of  what  we  know  as  their 
free  will .  Such  investigators  to  be  consistent  deny  that  there 
is  such  a  thing  as  free  will,  but  that  all  the  multiplied  inter- 
changes of  sensation  and  volition  are  just  so  many  neces- 
sary causes  and  effects.  On  the  other  hand,  other  observers, 
usually  without  much  scientific  training,  at  one  blow  divorce 
consciousness  from  all  forms  of  brain  activity  and  hold  it  to 
be  perfectly  aloof  and  independent  from  changes  which 
occur  in  nervous  cells.  To  such  individuals  the  brain  is  a 
secondary  organ  and  its  function  somewhat  questionable. 
Possibly  the  true  ground  lies  somewhere  between  the  two. 
It  is  the  simplest  every-day  observation  that  states  of  con- 
sciousness are,  so  far  as  we  know,  indissolubly  locked  with 
states  of  brain.  On  the  other  hand,  it  seems  in  violation  of 
all  knowledge  that  consciousness  is  but  a  necessary  physical 
result  from  the  clash  of  nervous  molecules.  From  the 
standpoint  of  physiology  it  is,  however,  well  to  remember 
that  with  this  question,  interesting  as  it  may  seem,  we  have 
in  this  field  at  present  nothing  to  do. 

SLEEP. 

The  lower  centers  of  the  brain,  the  mid-brain  and  spinal 
cord,  and  of  course  the  sympathetic  system,  are  in  con- 
tinued physiological  activity.  At  no  time  during  the  normal 
existence  of  the  individual  are  the  physiological  functions 


466  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

of  these  centers  suspended  for  a  moment.  In  the  higher 
conscious  centers  of  the  brain  there  is,  however,  a  marked 
exception.  At  certain  periods  there  supervenes  what  we 
familiarly  designate  as  "sleep."  This  common  phenomenon 
so  easily  experienced  is  nevertheless  one  of  the  most  difficult 
of  explanation,  and  we  are  at  present  entirely  at  a  loss  to 
understand  what  the  exact  nature  of  sleep  is.  We  know 
that  it  concerns  only  the  higher  conscious  centers.  The 
reflex  centers  below  are  in  their  regular  activity,  unless  we 
should  modify  this  by  the  statement  that  during  sleep  the 
activities  here  are  sometimes  reduced,  but  never  suspended. 

Going  to  sleep  is  a  sudden  thing,  although  it  is  preceded 
by  a  short  period  in  which  the  sensations  become  gradually 
dimmed.  Waking  up,  too,  is  a  somewhat  sudden  event. 
What  an  interesting  question  it  would  be  to  determine,  if 
possible,  just  what  occurred  when  sleep  suddenly  super- 
venes or  when  later  on  with  similar  suddenness  conscious- 
ness returns.  It  is  held  by  some  physiologists  that  sleep 
results  when  no  impressions  reach  the  brain.  This,  of 
course,  is  at  once  faulty  in  its  general  application,  because 
it  is  possible  to  go  to  sleep  even  amidst  a  confusion  of  noises 
and  sensations.  On  the  other  hand,  however,  experiments 
have  been  made  with  animals  with  paralyzed  sensory  nerves 
and  which  were  in  addition  to  this  blind  and  deaf  on  one 
side.  When  under  such  circumstances  the  only  remaining 
sources  of  sensation  to  the  brain,  that  is,  the  opposite  eye 
and  ear  were  closed,  the  animal  at  once  dropped  to  sleep 
and  awakened  as  soon  as  these  avenues  of  impression  were 
opened. 

It  has  been  suggested,  but  only  as  a  suggestion  and  not 
a  scientific  fact,  or  even  theory,  that  sleep  may  result  from 
the  slight  withdrawal  of  the  dendrons  surrounding  the  cere- 
bral cells.  It  is,  of  course,  conceivable  that  these  dendrons 
might  separate  to  a  slight  extent,  possibly  separate  so  far  as 
to  make  the  transmission  of  an  impulse  more  difficult,  and 
that  this  separation,  like  the  opening  of  the  switch  on 
a  switch  board  would  produce  a  cessation  of  the  flow  of 


ANATOMY,   PHYSIOLOGY,   OF  NERVOUS  SYSTEM.          467 

impulses,  and  so  produce  sleep,  and  that  waking  would 
consist  in  the  moving  together  of  these  dendrons  and  so 
re-establishing  the  natural  flow  of  impulses. 

During  sleep  the  entire  range  of  conscious  centers  may 
not  be  affected.  Sometimes  certain  centers  or  portions  of 
certain  centers  seem  to  remain  awake,  and  then  these  cen- 
ters, relieved  from  the  controlling  influences  of  neighboring 
centers  run  riot  and  give  rise  to  the  production  of  dreams. 
When  the  centers  so  awake  happen  to  be  motor  centers 
there  may  be  produced  forms  of  sleep  in  which  more  or  less 
extended  movements  occur  familiar  to  us  under  the  name  of 
somnambulism . 

That  sleep  is  not  due  to  the  lack  of  blood  in  the  brain, 
and  so  be  a  phenomenon  like  fainting,  is  easily  disproved 
by  experiments  which  show  that  the  blood  supply  in  the 
brain  while  asleep  sinks  very  little  below  the  normal. 

HYPNOTIC  PHENOMENA. 

Hypnotism  is  by  many  looked  upon  as  an  abnormal 
variety  of  somnambulism.  There  is,  however,  connected 
with  this  subject  of  hypnotism  so  much  that  is  questionable 
and  suspicious  along  with  the  little  that  is  real  and  scientific, 
that  it  is  exceedingly  difficult  to  come  to  definite  scientific 
conclusions.  It  is  explained  by  some  as  a  peculiar  sleep, 
and  looked  upon  by  others  as  a  mere  form  of  embarrassment 
and  frightened  imagination. 

TIME  RELATIONS  IN  PSYCHIC  PHENOMENA. 

That  mental  processes  take  a  certain  amount  of  time  is 
an  e very-day  observation.  The  exact  measurement  of  simple 
and  definite  psychical  acts  was  first  made  as  a  result  of  the 
observation  that  astronomers  of  equal  care  and  precision 
did  not  record  the  passage  of  a  star  across  the  hairs  of 
their  observing  telescopes  at  the  same  instant.  This  differ- 
ence in  time  was  at  first  attributed  to  a  greater  or  less  care- 
lessness in  the  observer.  Repeated  experiments  soon  showed 
that  there  was  a  difference  in  time  even  when  both  observers 


468  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

had  with  the  greatest  precision  noted  the  transit  just  at  the 
moment  they  saw  it  in  the  telescope.  These  little  differ- 
ences of  time  were,  therefore,  due  to  the  differences  of  time 
in  the  nervous  systems  of  the  observers,  and  so  it  became 
necessary  to  find  out  for  each  observer  the  time  that  he 
required  to  record  the  observation.  This  was  called  his 
personal  equation. 

In  the  field  of  physiological  psychology  a  great  deal  of 
work  has  been  done  in  determining  the  reaction  time  of  the 
various  centers.  This  is  the  interval  between  the  percep- 
tion of  anything  and  its  interpretation.  A  multitude  of 
books  are  available  everywhere,  and  it  seems  undesirable 
in  this  treatise  to  enter  in  detail  into  this  field.  Interesting, 
however,  .are  the  points  that  this  reaction  time  may  be 
shortened  by  practice,  and  that  the  reaction  time  may  in  a 
general  way  be  taken  as  a  physiological  index  of  the 
individual's  education  of  the  sense  in  question.  It  is  of 
course  understood  that  the  reaction  time  for  complicated 
psychical  processes  will  be  correspondingly  longer  than  for 
simpler  ones,  and  that  they  need  not  necessarily  be  the 
same  for  the  different  sense  organs.  The  shortest  re- 
action time  is  possibly  that  of  the  eye.  The  further  large 
field  of  interesting  observations  which  has  to  do  with  the 
interpretation  of  sensations  and  their  association  in  memory 
must  here  be  referred  to  the  field  of  physiological  psychology 
in  which  the  advances  have  in  recent  years  been  so  great  as 
to  rank  that  science  as  one  of  the  co-ordinate  biological 
sciences  of  the  day,  whose  field  has,  therefore,  by  the 
necessities  of  such  an  extension  been  more  or  less  excluded 
from^purely  physiological  considerations. 


CHAPTER  XX. 


THE  ORGANS  OF  SPECIAL  SENSE. 

Whenever  the  sensory  nerves  in  any  part  of  the  body  are 
properly  affected,  a  nervous  impulse  arises  which  is  then 
conveyed  to  the  inner  centers  and  may  there  give  rise,  and 
usually  does  give  rise,  to  what  we  ordinarily  call  a  sensa- 
tion. Very  few  tissues,  indeed,  in  the  body  do  not  have 
this  property  of  sensation.  These  are  the  hairs,  the  nails, 
portions  of  cartilage  and  bone,  and  other  forms  of  con- 
nective tissue,  but  with  these  obvious  exceptions  every 
tissue  in  the  body  is  able  to  produce  by  its  proper  nerves, 
changes  and  sensations  in  the  brain. 

Sensations,  however,  differ  at  once  fundamentally  and 
fall  into  two  groups.  In  one  group  we  have  the  sensations 
which  give  states  of  feeling  of  our  own  body  usually  with- 
out any  relation  at  all  to  the  outer  world.  The  other  sen- 
sations seem  to  be  projected  beyond  the  body  into  the 
external  world  and  produce  in  us  ideas  concerning  the 
phenomena  of  our  own  environment.  Thus,  we  have  the 
common  sensations  of  the  body  and  the  special  sensations. 

The  common  sensations  are  the  general  feelings  of  pain, 
of  hunger  and  thirst,  fatigue  and  buoyancy  and  possibly  all 
the  varied  feelings  accompanying  disease.  In  no  instance 
probably  are  these  feelings  ever  projected  into  the  world  of 
things.  From  these  we  gain  absolutely  no  notion  of  our 
environment. 

In  the  second  class  belong  the  sensations  which  are 
produced  by  the  organs  of  special  sense  and  those  general 
sensations  of  touch  in  so  far  as  they  give  to  us  knowledge 
of  external  things.  It  is  with  these  latter  sensations  that 
this  chapter  concerns  itself. 

There  is  possibly  not  a  hard  and  fast  line  dividing 
special  sensations  from  the  common  sensations.  Thus,  for 

(469) 


470  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

instance,  a  slight  pressure  on  the  finger  gives  an  idea  of 
the  nature  of  the  object  touched.  A  material  increase  of 
such  a  pressure  produces  pain  and  no  longer  helps  \\s  in 
understanding  the  environment.  If  in  the  case  of  the  eye 
a  normal  amount  of  light  gives  perceptions  of  sight,  an  ex- 
cessively strong  light  blinds  and  hurts.  It  is  probable  that 
many  forms  of  pain,  if  not  all  of  them,  are  excessive  stim- 
ulations of  the  nerves.  On  the  other  hand  it  is  possible, 
especially  with  the  sense  of  touch  to  make  the  stimulation 
of  the  nerves  so  slight  as  to  render  a  distinct  perception 
difficult.  The  resulting  sensations  in  such  a  case  we  com- 
monly designate  as  those  of  a  tickling  or  irritating  nature. 

THE  STRUCTURE  OF  AN  ORGAN  OF  SPECIAL  SENSE. 

The  ordinary  phenomena  of  the  external  world  do  not 
as  a  rule  affect  nerves  directly.  In  order  to  have  such 
phenomena  produce  a  nervous  impulse  it  is  necessary  to 
provide  the  nerve  with  some  form  of  specially  adapted  ap- 
paratus which  shall  receive  the  external  impressions  and 
translate  or  manipulate  them  in  such  a  way  as  to  give  rise 
to  a  nervous  impulse.  In  fact  the  difference  between  nerves 
of  special  sense  and  the  ordinary  nerves  of  the  body  lies  in 
this  fact.  Thus  we  have  for  an  optic  nerve  the  special  ap- 
paratus of  the  eye,  the  retina,  for  the  auditory  nerve  the 
labyrinth  of  the  ear,  and  for  the  special  sense  of  touch 
peculiarly  adapted  corpuscles  and  end  bulbs.  The  first 
requisite,  therefore,  is  a  specially  adapted  end  organ. 
These  end  organs  are  in  turn  differentiated  among  them- 
selves, one  being  adapted  to  one  particular  kind  of  external 
impressions,  such  as  light,  say,  another  constructed  on  an 
entirely  different  plan  so  as  to  catch  the  vibrations  of  sound. 
A  third  so  arranged  as  to  be  easily  affected  by  changes  in 
pressure. 

But  these  end  organs  serve  merely  to  start  the  nervous 
impulses.  They  do  not  produce  sensations  of  sight,  hear- 
ing or  touch.  In  fact,  the  nervous  impulses  running  along 
the  optic  nerve,  the  auditory  nerve  or  touch  nerve  are  in  all 


THE   ORGANS   OF   SPECIAL  SENSE.  471 

probability  perfectly  identical,  and  the  reason  that  one  gives 
rise  to  sensations  of  light,  the  other  to  those  of  sound,  and 
a  third  to  perceptions  of  touch  is  not  due  to  any  difference 
in  these  impulses,  but  is  due  to  the  centers  in  the  brain  in 
which  they  end.  Although  such  a  thing  is  entirely  impos- 
sible in  reality  it  is  possible  to  imagine,  and  justly  so,  that 
if  the  auditory  nerve  could  be  made  to  run  to  the  visual 
center  in  the  brain,  sound  would  be  interpreted  as  light, 
while  if  the  optic  nerve  should  end  in  the  upper  temporal 
lobe,  colors  would  be  interpreted  as  sounds. 

A  complete  organ  of  special  sense,  then,  is  a  special 
nerve  center  in  the  brain  and  a  special  apparatus  at  the 
distal  end  of  a  nerve  connected  with  it.  The  phenomena 
of  the  special  sensations  therefore  naturally  fall  into  two 
kinds:  the  phenomena  that  take  place  in  the  end  organs, 
and  those  that  take  place  in  the  brain.  Our  knowledge  of 
the  processes  which  occur  in  the  brain  center  is  from  a  phy- 
siological standpoint  so  meager  that  for  evident  reasons  it  is 
here  omitted  altogether.  Pure  physiology  concerns  itself 
now  mainly  with  those  nervous  changes  which  occur  at  the 
distal  end  of  the  nerve.  We  may  speak  of  a  complete  sen- 
sation consisting  of  two  events;  the  first,  a  neurosis  —  a 
nervous  impulse  of  some  kind  produced  in  a  special  way  in 
a  special  end  organ  and  conveyed  along  a  nerve  to  a  special 
center  in  the  brain.  The  second  event,  the  psychosis,  a 
conscious  perception  and  interpretation  of  this  nervous  state 
as  a  sensation.  It  is  difficult  here  to  avoid  confusion  in 
the  employment  of  the  word  tc  sensation. "  Frequently  it 
is  used  to  include  both  the  nervous  changes  and  the  psycho- 
logical results  which  it  calls  forth.  At  other  times  the  word 
"sensation"  is  used  to  designate  merely  the  psychological 
result.  The  reader  must  himself  judge  carefully  from  the 
context  in  which  the  word  occurs  what  application  is  given 
to  the  term. 

The  neurosis  is  always  the  cause  of  the  psychosis,  unless 
one  should  except  certain  forms  of  mental  hallucination 
which  appear  so  real  to  the  person  as  to  be  objectified. 


472  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

While  this  relation  of  cause  and  effect  is  absolutely  clear,  it 
is  equally  clear  that  there  is  not  a  bit  of  similarity  between 
the  neurosis  and  the  psychosis.  In  other  words,  vibrations 
in  the  internal  ear,  or  even  the  nervous  impulses  which 
such  vibrations  produce  are  absolutely  different  in  kind  from 
those  psychological  sensations  which  we  designate  as  sound, 
and  there  is  clearly  no  similarity  between  an  ethereal  vibra- 
tion or  the  stimulation  of  a  rod  or  cone  in  the  eye  and  what 
we  psychologically  call  light.  Between  the  two  there  is  a 
chasm  that  cannot  at  present  be  bridged,  and  so  all  at- 
tempts at  explanation  are  useless  and  out  of  place.  To 
prove  the  assertion  that  there  is  no  similarity  in  essence  be- 
tween physical  light  and  psychological  sensation  of  light  one 
needs  only  to  be  reminded  that  the  psychological  sensation 
of  light  can  easily  be  produced  when  no  physical  light  is 
present.  One  needs  only  to  be  struck  on  the  head  or  to 
have  the  optic  nerve  stimulated,  electrically  or  otherwise,  to 
perceive  in  the  most  emphatic  and  clearest  way  sensations 
interpreted  as  those  of  light.  The  stimulation  of  the  audi- 
tory nerve  will  produce  a  ringing  noise  in  a  perfectly 
quiet  medium. 

To  summarize,  then,  sensations  differ  in  their  modes  or 
modality,  a  difference  caused  by  the  centers  in  the  brain  to 
which  they  go.  Of  the  sensations  of  a  separate  and  distinct 
mode,  such  as  those  of  sight,  there  may  be  distinctions  in 
quality,  such  as  those  of  red,  green  or  blue  lights,  or  in  in- 
tensity, such  as  a  strong  or  faint  light.  There  may  be  dif- 
ferent qualities  which  we  recognize  as  differences  in  touch, 
or  different  intensities  which  we  recognize  in  loudness  or 
softness.  The  modality  of  a  sensation  is  determined  by  the 
brain  center  to  which  the  nerve  goes,  while  the  quality  and 
the  intensity  of  the  sensations  of  the  single  modality  are 
normally  determined  by  the  end  organ  itself. 

THE  DEVELOPMENT  OF  THE  SPECIAL  SENSES. 

From  an  anatomical,  especially  an  embryological  point 
of  view,  it  is  at  once  apparent  that  the  special  sensations 


THE   ORGANS   OF   SPECIAL  SENSE.  473 

are  but  special  modifications  of  the  general  sensations  of 
the  body.  In  fact,  comparative  anatomy  could  even  in 
such  a  complicated  structure  as  an  eye  find  between  the 
highly  developed  human  eye  and  the  mere  pigment  spot  in 
the  skin  of  some  of  the  lowest  animals  many  intervening 
gradations.  The  little  pigment  spot  at  the  tip  of  the  ray  of 
the  starfish  which  enables  that  animal  to  detect  possibly 
the  direction  of  the  light  merely,  is  but  a  slight  advance  in- 
deed from  the  property  of  general  sensations  possessed  by 
its  entire  nervous  system.  The  localization  of  the  pigment 
at  other  points  than  those  of  the  tip  of  the  ray  might  suffice 
to  arouse  light  sensations.  Such  exceedingly  simple  forms  of 
eye,  were,  however,  in  the  development  of  the  animal  forms 
more  and  more  expanded,  specialized  and  complicated,  un- 
til finally,  from  a  somewhat  common  sensation,  there  re- 
sults the  highly  modified  retina  of  the  eye  with  its  acces- 
sories. 

THE  OBJECTIFICATION  OF  OUR  SENSATIONS. 

If  it  is  true  that  special  sensations  are  but  specialized 
general  sensations,  the  question  naturally  arises  why  such 
special  sensations  should  be  referred  to  the  external  world, 
whereas  the  general  sensations  are  not  so  referred.  The 
answer  to  this  is  at  hand.  It  is  among  the  simplest  obser- 
vations on  children  or  adult  defective  people  to  show  that 
these  special  sensations  are  at  first  not  objectified.  The 
reference  of  our  sensations  to  the  external  world  is  gradual 
and  the  result  of  our  early  education  and  experience.  In 
the  case  of  touch,  for  instance,  an  object  is  brought  in  con- 
tact with  the  skin  and  a  sensation  results.  By  repeated  ob- 
servation it  has  been  found  that  such  a  sensation  comes  from 
the  foot,  say.  This  the  individual  has  found  by  observing 
possibly  an  object  lying  on  his  foot.  Removing  the  same, 
he  noted  the  cessation  of  the  sensation.  In  this  way  he 
finally  infers  when  he  feels  this  same  sensation  that  it  must 
come  from  the  foot.  These  inferences  become  so  trust- 
worthy finally  to  the  individual  that  he  does  not  realize  at 


474  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

all  that  they  are  mere  mental  inferences,  but  he  seems  ac- 
tually to  feel  the  sensation  in  his  foot. 

What  is  true  of  the  sensation  of  touch  might  be  equally 
applicable  to  all  the  other  senses.  That  the  reference  of 
our  sensations  is  a  mere  matter  of  inference  may  be  proved 
by  the  fact  that  the  "seeing  of  stars"  (which  results  from 
a  blow  on  the  head)  is  projected  through  the  eyes  into  the 
external  world.  A  blow  on  the  ulnar  nerve  at  the  elbow 
(the  crazy-bone)  results  in  a  sensation  which  is  referred  not 
to  the  elbow  where  it  arose,  but  to  the  fingers  and  hand. 
This  mistake  occurs  from  the  fact  that  the  brain  has  been 
accustomed  to  believing  that  all  sensations  carried  by  the 
ulnar  nerve  come  from  the  hand.  The  truth  of  this  belief 
has  been  established  to  the  brain  over  and  over  again,  and 
so  when  this  impulse  reaches  the  brain  along  the  ulnar 
nerve  it  is  without  question  referred  to  the  same  place,  and 
this  reference  by  the  brain  is  so  distinct  and  real  that  it  is 
really  hard  to  believe  that  the  pain  is  not  actually  in  the 
fingers. 

That  the  reference  of  our  sensations  to  the  external 
world  is  a  matter  of  acquirement  is  proved  further  by  the 
possibility  of  educating  the  brain  in  this  matter.  Blind 
people  who  rely  much  more  upon  their  sense  of  touch  be- 
come remarkably  proficient  in  localizing  touches,  even  to 
the  extent  of  being  able  to  read  raised  print  rapidly  and  ac- 
curately with  their  finger  tips.  It  is  also  stated  that  per- 
sons who  had  been  blind  and  whose  eyesight  was  suddenly 
restored,  by  some  kind  of  operation  probably,  did  not  at 
first  see  objects  at  a  distance,  but  referred  all  of  their 
visual  sensations  to  the  eye  itself.  Such  persons  felt  a 
distant  tree,  not  as  an  object  of  the  external  world,  but  as 
a  peculiar  and  new  sensation  in  the  eyeball. 

THE  RELATION  BETWEEN  NEUROSIS  AND  PSYCHOSIS. 

It  was  just  pointed  out  that  there  is  the  relation  of  cause 
and  effect  between  the  nervous  excitation  in  the  end  organ 
and  the  mental  change  in  the  brain.  There  is  a  relation  of 


THE   ORGANS   OF   SPECIAL   SENSE.  475 

cause  and  effect  between  the  excitation  of  the  retina  under 
the  influence  of  light  and  the  conscious  perception  of  light 
in  the  brain.  Attempts  have  been  made  to  establish  a 
mathematical  relation  between  the  two.  That  there  is  some 
kind  of  a  quantitative  relation  between  the  two  is  probable,  for 
we  know  that  a  stronger  stimulation  of  the  retina  by  stronger 
light  causes  a  stronger  sensation.  A  harder  stroke  on  the 
piano  causes  an  increased  loudness  in  our  mental  percep- 
tion. Two  weights  resting  on  the  hand  are  perceived  more 
strongly  than  one.  The  question,  however,  is,  what  is,  in 
mathematical  terms,  this  definite  relation.  Several  attempts 
have  been  made  by  means  of  extended  experiments  on  the 
various  sense  organs  to  determine  such  a  mathematical 
relation,  the  most  noteworthy  being  that  of  the  celebrated 
psychologist  Fechner  and  known  as  Fechner's  " Psycho- 
physical  L,aw. ' '  This  Psycho-physical  law  is,  however,  only 
a  modification  of  the  psycho-physical  law  of  the  physiologist 
Weber,  whose  work  on  the  special  senses  is  one  of  the 
classics  on  that  subject.  This  psycho-physical  law  says  that 
when  the  stimuli  affecting  the  end  organs  vary  in  a  geometric 
ratio  the  intensity  of  the  subjective  sensation  varies  in  an 
arithmetical  ratio.  That  is,  if  five  units  of  light  would  pro- 
duce a  sensation  one,  then  to  produce  a  sensation  twice  as 
strong  requires  twenty-five  lights.  To  increase  the  subjec- 
tive perception  of  the  intensity  of  the  light  to  three  times 
its  original,  would  require  one  hundred  and  twenty-five 
lights.  Or,  to  state  the  law  in  another  way,  the  subjec- 
tive sensation  increases  directly  as  the  logarithm  of  the 
strength  of  the  stimulus. 

While  this  law  is  applicable  in  many  instances  it  is  seri- 
ously at  fault  in  others.  For  instance,  if  one  looks  at  a 
line  five  inches  in  length  and  then  wants  a  sensation  of  a 
line  twice  as  long  it  is  of  course  nonsense  to  say  that  that 
must  be  twenty-five  inches  in  order  to  appear  twice  as  long. 
It  approaches,  however,  the  truth  of  things  in  connection 
with  the  eye  and  ear.  Every  one  knows  that  two  candles 
in  a  room  do  not  make  it  twice  as  light  as  one.  candle. 


476  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

Two  voices  do  not  sound  twice  as  loud  as  one.  The 
experiment  may  be  easily  tried  in  a  room  where  there  are 
several  gas  jets.  After  one  jet  has  been  lighted  and  the 
intensity  of  the  illumination  of  the  room  noted,  it  will  take 
a  number  of  additional  gas  jets  to  make  the  room  seem 
doubly  as  light. 

CONFUSION  OF  SENSATIONS  AND  INFERENCES  FROM 
SENSATIONS. 

Many  of  our  so-called  special  sensations  are  really  not 
sensations  at  all,  but  are  inferences.  To  see  the  height  of 
a  tree  is  an  inference;  to  see  the  solidity  of  an  object  is  an 
inference;  distance  is  wholly  a  matter  of  judgment,  and  the 
perception  of  size  a  mere  comparison.  It,  therefore,  not 
infrequently  happens  that  our  sensations  mislead  us.  In 
justice  to  the  sensations,  however,  which  in  a  normal  body 
probably  never  mislead  but  invariably  tell  the  truth,  it  ought 
to  be  said  that  it  is  not  the  sensations  themselves  which  mis- 
lead, but  the  inferences  which  we  choose  to  draw  from  them. 
In  calling  attention  to  these  inferences  it  is  not  the  purpose 
here  to  carry  the  argument  so  far  as  to  say  with  certain 
philosophers  that  everything  is  an  inference  and  nothing  a 
matter  of  knowledge ;  that  to  see  a  certain  color  plainly 
with  the  eye  is  not  a  trustworthy  bit  of  knowledge,  but  a 
mere  inference  drawn  from  a  certain  state  of  the  body. 
With  this  Cartesian  philosophy  physiology  does  not  concern 
itself,  and  the  sensations  which  arise  in  the  body  normally 
in  every  way  are  treated  at  once  as  trustworthy  bits  of 
knowledge  from  which  as  premises  true  inferences  may 
logically  be  drawn. 

The  special  sense  organs  are  discussed  in  the  following 
chapters  in  the  order  of  their  complexity,  the  simplest  being 
taken  first. 


CHAPTER  XXI. 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE, 
TASTE,  SMELL. 

It  was  long  known  that  sensations  of  touch  were  brought 
about  by  the  stimulation  of  sensory  nerves  and  that  the 
section  of  such  nerves  destroyed  the  sensation,  but  it  was 
rather  late  before  the  special  end  organs  of  touch  were  dis- 
covered. The  first  known  end  organs  of  touch  were  the 
Pacinian  corpuscles,  discovered  by  Vater  in  1741.  The 
touch  corpuscles  were  not  discovered  until  1852,  when  they 
were  described  by  Wagner  and  Meissner.  It  was  in  1846, 
however,  when  E.  H.  Weber  published  his  work  that  physi- 
ologists arrived  at  the  present  conception  of  the  sensation 
of  touch  and  temperature. 

THE  ANATOMY  OF  THE  END  ORGANS  OF  TOUCH. 

Every  part  of  the  skin  is  sensitive,  being  supplied  with 
sensory  nerves.  Usually  these  nerve  fibers  end  in  plexuses, 
the  final  terminations  of  which,  in  the  form  of  little  fibrils, 
which  have  lost  their  medullary  coat,  end  in  the  dermis,  or 
may  reach  even  in  among  the  cells  of  the  Malpighian  layer 
of  the  epidermis  and  there  terminate  without  any  special 
end  organ.  In  those  portions  of  the  skin,  however,  where 
the  sensation  of  touch  is  specialized  special  end  organs  are 
found.  These  are  of  several  kinds: 

1. —  The  Pacinian  Corpuscles.  These,  as  just  stated, 
were  the  first  discovered,  a  fact  due,  no  doubt,  to  their 
relatively  large  size,  ranging  from  a  fifteenth  to  a  tenth  of 
an  inch  in  length.  In  the  transparent  omentum  of  the  cat 
they  are  readily  recognized  with  the  unaided  eye  as  little 
whitish  translucent  bodies.  They  are  found  in  large  num- 
bers in  the  areolar  tissue  under  the  skin  of  the  hand  and 

(477) 


478 


STUDIES   IN   ADVANCED   PHYSIOLOGY 


foot   and   occasionally   elsewhere,  as  in   tendons  and  liga- 
ments, or  (especially  true  of  the  cat)  in  the  mesentery.     A 


Fig.  149.— A  PACINIAN  CORPUSCLE   FROM  THE  CAT'S  MESENTERY.     (After  Ranvier.) 
n,  nerve;  n',  its  continuation  through  the  core  m;  a,  termination  of  nerve  in  distal 
end;  d,  ct  coats  or  capsules;  /,  a  channel  for  the  nerve. 

Pacinian  corpuscle  is  made  up  of  a  body  of  connective  tissue 
which  shows  quite  a  number  of  concentric  rings.  These 
rings  are  really  capsules.  If  one  were  to  imagine  a  great 
number  of  egg  shells  placed  one  within  another  and  the 
space  between  the  contiguous  egg  shells  filled  with  a  little 
liquid  the  analogy  to  the  Pacinian  corpuscle  would  be  appar- 
ent. In  the  center  of  these  concentric  capsules  there  is  a 
soft  core  in  which  a  nerve  fiber  ends. 

2. — The  tactile  cells.  The  tactile  cells  seem  nothing  more 
than  specialized  cells  of  the  lower  layers  of  the  epidermis. 
In  regions  of  the  skin  where  sensation  is  very  acute  there 
are  found  near  the  Malpighian  layer  certain  cells  which 
seem  to  stain  more  deeply,  are  larger,  more  oval  and  more 
granular  than  the  ordinary  epidermal  cells.  Delicate  nerve 
fibers  can  be  traced  to  them  which,  according  to  some  ob- 
servers, end  in  networks  which  invest  these  tactile  cells  like 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE. 


479 


the  dendrons  in  the  spinal  cord  but  which,  according  to 
other  observers,  are  said  to  pierce  the  cells  and  end  directly 
in  them. 

3. — End  bulbs.     The  end  bulbs  are  found   especially  in 


Fig.  150.— END-BULBS  FROM  THE  HUMAN  CONJUNCTIVA.    (After  Longworth.) 
n,  nerve  running  to  end-bulbs. 

the  sensitive  conjunctiva.     The  sensory  fibers  which  reach 
the  cornea  branch  and  rebranch  into  finer  fibers  which  form 


Fig.   151.-— A  SINGLE  END-BULB,   MUCH  ENLARGED.      (After  L.ongWOrth.) 
a,  entering  nerve;  b,  capsule  containing'  nuclei;  c,  c,  portions  of  the  nerve  within  cut 
across;  d,  et  cells  making  up  the  core. 

a  kind    of    network    in    the    cornea.     From    this  network 
branches  go  into  the  epithelium  of   the  conjunctiva,  pierce 


480 


STUDIES    IN   ADVANCED    PHYSIOLOGY. 


it  and  end  on  the  outer  surface  of  the  conjunctiva  in 
little  bulb-like  terminations  which  float  in  the  tears.  The 
statement  of  Conheim  that  these  end  bulbs  actually  project 
from  the  cornea  and  float  in  the  lachrymal  fluid  which  con- 
tinually bathes  the  cornea  explains  very  satisfactorily  the 
extreme  sensitiveness  of  the  conjunctiva.  Other  observers, 
however,  deny  that  these  end  bulbs  actually  project  above 
the  cornea,  but  hold  that  they  are  imbedded  in  the  surface 
epithelium  of  the  cornea.  Similar  end  bulbs  occur  in  the 
lips  and  the  mouth. 

4. — The  touch  corpuscles.  The  touch  corpuscles  are 
probably  the.  most  important  of  all  the  tactile  end  organs, 
as  they  are  found  in  large  numbers  in  the  skin  of  the  hands 


Fig.  152. — SECTION  OF  THE  SKIN  SHOWING  TWO  PAPILLAE,  ONE  CONTAINING  A  CAPILLARY 

LOOP  O,   THE   OTHER   CONTAINING   A   TACTILE   CORPUSCLE.      (After  Biesiadecki.) 

d,  entering  nerve  of  three  fibers ;   /,  /,  three  fibers  cut  within  the  corpuscle.    The 
fibrous  connective  tissue  capsule  is  plainly  shown. 

and  toes,  regions  which  are  most  frequently  used  as  organs 
of  touch.  They  do,  however,  occur  in  other  places  such, 
for  instance,  as  the  forearm,  lips  and  tongue.  The  ex- 
treme sensitiveness  of  the  nipple  is  due  to  these  same  cor- 
puscles. They  lie  in  the  dermis  where  the  papillae  extend 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE.  481 

up  into  the  epidermis,  which  papillae  cause  the  character- 
istic arrangement  of  the  fine  lines  so  readily  discernible  in 
the  palm  of  the  hands  and  fingers.  Some  of  the  papillae 
contain  blood-vessels,  but  the  majority  of  them  contain 
touch  corpuscles  so  that  by  examining  these  little  ridges  on 
the  hand  one  is  able  to  trace  real  rows  of  these  tactile  cor- 
puscles imbedded  just  beneath.  They  are  quite  small,  be- 
ing only  3^0"  of  an  inch  in  length.  In  outline  they  are  oval 
and  consist  of  a  capsule  of  connective  tissue  fibers  wound 
round  and  round.  One  or  more  nerve  fibers  reach  each 
corpuscle,  and  after  making  several  turns  around  it  enter 
the  capsule  losing  at  that  point  their  medullary  coats.  The 
axis  cylinder,  however,  penetrates  the  connective  tissue 
capsule,  branches  several  times  and  ends  in  little  bulb- 
shaped  enlargements  among  the  meshes  of  the  same. 

Possibly  the  explanation  of  the  action  of  all  these  end 
organs  lies  in  the  fact  that  any  pressure  on  such  a  corpuscle 
would  be  much  more  likely  to  be  transmitted  by  it  to  the 
contained  nerve,  just  as  fingers  placed  between  two  boards 
would  be  much  more  likely  to  notice  an  increase  of  pres- 
sure near  them  than  if  not  so  situated. 

A  very  interesting  form  of  touch  corpuscles,  although 
not  found  in  the  human  body,  occurs  in  the  beak  of  certain 
birds,  such  as  the  duck.  A  corpuscle  here  consists  of  a 
capsule  of  connective  tissue  in  which  lie  several  cuboidal 
cells  one  above  the  other  somewhat  like  several  bricks 


n 

Fig.  153.— CORPUSCLE  OF  GRANDRY  FROM  THE  DUCK'S  TONGUE.    (After  Izquierdo.) 
n,  nerve. 

might  be  stacked  in  a  row.  A  nerve  penetrates  the  cap- 
sule and  sends  off  branches  which  finally  end  between  these 
cells.  No  doubt  a  pressure  transmitted  to  this  corpuscle  is 


482  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

transmitted  by  the  cells  more  effectively  to  the  delicate 
nerve  filaments  between  them.  Just  like  a  finger,  to  use 
the  same  illustration  again,  would  be  more  susceptible  if 
placed  between  bricks  in  such  a  row.  This  variety  of 
touch  corpuscle  is  designated  as  Grandry's  corpuscle. 

THE  ABSOLUTE   TOUCH  SENSITIVENESS. 

By  the  term  of  absolute  sensitiveness  is  generally  under- 
stood the  minimum  stimulus  which  is  yet  able  to  produce  a 
sensation  at  the  particular  point  in  question.  All  parts 
of  the  skin  have  not  the  same  absolute  sensibility.  Things 
which  at  certain  portions  produce  no  sensation  at  all  are 
at  other  places  perceived  with  the  greatest  clearness.'  The 
highest  absolute  sensibility  seems  to  be  on  the  forehead, 
where  a  minimum  pressure  of  no  more  than  .002  of  a  gram 
is  sufficient  to  produce  a  sensation.  On  the  temples  about 
.05  of  a  gram;  on  the  lower  lip  and  fingers  .5  of  a  gram, 
on  the  forearm  it  requires  9  grams  and  on  the  skin  of  the 
thigh  as  much  as  17  to  20  grams. 

If  instead  of  allowing  a  weight  to  rest,  as  was  the  case 
in  the  determination  of  the  figures  just  given,  one  should 
take  a  hair  or  bristle  of  known  stiffness  and  that  should  be 
moved  across  the  skin  in  question,  the  minimum  pressure 
perceivable  is  much  reduced.  In  such  experiments  the 
forehead  perceives  a  pressure  as  little  as  .0007  of  a  grain;  on 
the  arm  or  leg  about  .06.  These  figures  of  course  corre- 
spond with  the  experience  of  every  one  that  the  forehead, 
skin  of  the  face  generally,  the  lips  and  fingers  are  able  to 
perceive  differences  in  pressure  which  are  entirely  out  of 
the  question  on  most  other  portions  of  the  body. 

THE  POWER  OF  LOCALIZATION  AND  THE  TOUCH  AREAS. 

The  power  to  localize  a  touch  sensation  is  a  result  of 
experience.  It  may  be  materially  improved  by  practice 
but,  other  things  being  equal,  the  varioiis  portions  of  the 
skin  show  naturally  a  very  different  localizing  ability.  Thus, 
at  the  tip  of  the  tongue  two  points  as  close  together  as 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE.  483 

one  millimeter  may  still  be  perceived  as  distinct  points; 
at  the  tip  of  the  finger  we  perceive  as  two  objects,  points 
as  close  as  two  millimeters ;  on  the  wrist  and  arm  the  power 
to  localize  becomes  much  less  and  a  distance  of  four  or  five 
millimeters  apart  hardly  produces  a  double  sensation.  The 
lips  require  4  mm. ;  the  tip  of  the  nose  6  mm. ;  the  eyeball 
10  mm. ;  the  forehead  20  mm. ;  the  back  of  the  hand  28 
mm.,  and  the  middle  of  the  back  and  neck  require  as  much 
as  60  mm.  between  the  two  points  to  be  perceived  as  double. 
That  the  absolute  sensibility  and  the  power  to  localize 
are  different  is  evident  in  the  case  of  the  forehead,  where 
absolute  sensibility  is  possibly  greater  than  in  any  other 
portion  of  the  skin,  but  where  the  power  of  localization  is 
only  possible  when  the  points  applied  are  as  much  as  20 
mm.  apart.  This  relative  power  of  localization  has  been 
generally  described  in  terms  of  touch  circles.  The  diam- 
eters of  such  circles  being  the  least  distance  between  two 
points  to  be  perceived  as  double.  The  touch  areas,  there- 
fore, on  the  point  of  the  tongue  are  exceedingly  small,  only 
1  mm.  in  diameter,  while  on  the  other  extreme,  the  touch 
circles  on  the  middle  of  the  back  are  as  much  as  60  mm.  in 
diameter.  Two  points,  then,  placed  within  such  a  circle 
are  perceived  as  one,  or  in  other  words,  to  perceive  two 
points  placed  on  the  skin  as  two,  requires  that  the  two 
points  shall  fall  in  different  touch  circles.  It  is  very  neces- 
sary, however,  to  remember  that  these  touch  areas  are  not 
definite  anatomical  structures,  and  that,  for  instance,  it  is 
quite  impossible  with  a  pencil  to  divide  the  skin  of  the  back 
into  such  circles  so  that  in  every  case  two  points  coming 
within  a  circle  would  produce  a  single  sensation,  or  placed 
in  adjacent  ones,  a  double  sensation.  For,  if  one  point 
should  be  placed  close  to  the  edge  of  one  such  area  and  the 
other  point  right  on  the  boundary  line  of  the  adjacent  area 
so  that  the  actual  distance  between  the  two  points  should 
be  less  than  60  mm.,  they  are  perceived  as  one.  It  is, 
therefore,  not  at  all  possible  that  the  existence  of  these  cir- 
cles are  brought  about  by  the  fact  that  each  circle  has 


484  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

a  single  nerve  going  to  it,  and  so  carries  but  a  single  im- 
pulse, no  matter  in  what  part  of  the  circle  it  is  stimulated. 
That  this  notion  is  wrong  is  clearly  proved  by  the  fact  that 
by  practice  this  circle  may  be  made  much  smaller,  a  thing 
which  would  be  utterly  impossible  if  they  were  anatomical 
units.  The  possible  explanation  is  that  the  nerves  coming 
from  certain  portions  of  the  skin  run  in  such  a  way  through 
the  centers  in  the  cord  or  brain  as  to  produce  more  of  a 
radiation  into  the  neighboring  fibers  or  cells,  and  so  prevent 
a  very  accurate  localization.  Practice  in  such  a  case  would 
be  merely  the  experience  to  eliminate  these  radiations  and 
to  be  able  to  define  the  sensation  at  last  to  the  exact  nerve 
fibers  in  question. 

It  is  given  by  some  observers  that  on  an  average  each 
touch  area  contains  about  twelve  touch  corpuscles.  If  this 
be  really  true,  the  explanation  of  these  touch  areas  may 
consist  in  the  possible  fact  that  the  stimulation  at  any  point 
stimulates  not  only  the  touch  corpuscle  immediately  under- 
neath or  next  to  it,  but  about  a  dozen  of  the  adjoining  ones, 
and  so  a  rather  compound  sensation  is  carried.  Where 
these  twelve  are  closely  huddled,  as  in  the  case  of  the 
tongue  or  lip,  the  power  to  localize  the  affected  spot  would 
be  quite  definite,  while  in  the  case  of  the  scattered  corpus- 
cles at  other  portions  of  the  skin,  the  area  would  be  too 
large  for  exact  definition. 

THE  SENSE  OF  TEMPERATURE. 

Not  only  is  the  skin  able  to  perceive  tactile  impressions 
but  it  is  also  able  to  take  note  within  certain  limits  of  the 
temperature  of  the  objects  affecting  it.  This  ability  to  per- 
ceive the  warmth  of  anything  is,  however,  not  an  absolute 
one  like  that  of  a  good  thermometer,  but  is  only  relative.  We 
are  only  able  to  tell  whether  a  thing  is  hotter  or  colder  than 
the  part  of  the  skin  affected,  or  when  the  comparison  is  en- 
tirely between  outside  objects  we  are  enabled  simply  to  de- 
termine of  these  which  is  the  warmer.  This  may  be  easily 
proved  by  immersing  one  hand  in  warm  water  and  the  other 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE.  485 

in  cold  water  for  some  time.  If,  now,  both  hands  be 
plunged  into  hike-warm  water  it  will  appear  warm  to  one 
hand  and  cold  to  the  other. 

The  ability  to  determine  differences  in  temperature  lies 
within  comparatively  narrow  limits.  A  reduction  of  a  tem- 
perature much  below  that  of  the  body  soon  produces  pain. 
An  elevation  of  a  temperature  much  higher  a  corresponding 
pain  or  burn.  The  finest  distinctions  in  temperature  are 
made  when  these  temperatures  are  about  those  of  the  body. 
Different  regions  of  the  body  show  different  abilities  to  per- 
ceive changes  in  temperature.  A  few  given  in  the  order  of 
their  ability,  beginning  with  the  best,  are,  the  point  of  the 
tongue,  eyelids,  cheeks,  lips,  neck.  It  is  interesting  to 
note  that  the  hands  and  feet  seem  to  follow  no  regular  rule 
at  all,  but  are  warm  or  cold  or  insensitive  under  the  most 
varying  conditions.  Possibly  this  is  the  result  of  the  ex- 
posure which  these  parts  surfer  almost  continually  to  the 
ever-changing  temperature  of  their  environment  and  so  be- 
come somewhat  dulled. 

The  sense  of  temperature  is  very  exactly  localized.  In 
fact,  changes  in  the  temperature  of  two  points  may  some- 
times aid  in  their  perception  as  two  when  otherwise  they 
would  have  been  perceived  as  single.  The  general  feel- 
ing of  cold  and  heat  are  not  really  sensations  of  the  en- 
tire body,  but  are  simply  extended  skin  sensations.  The 
body  feels  cold  when  the  skin  is  cold,  even  though  the 
interior  of  the  body  may  be  warm.  This,  for  instance, 
is  proved  by  the  chills  of  many  fevers,  which  chills  are 
usually  accompanied  with  an  actual  increase  of  inner  tem- 
perature. On  the  other  hand,  the  general  feeling  of  warmth 
which  the  toper  experiences  after  his  draught  is  really  not 
an  increase  of  bodily  heat  at  all,  but  is  simply  explained 
by  the  fact  that  under  the  action  of  alcohol  the  blood 
from  the  warmer  visceral  organs  is  driven  through  the  skin. 
As  an  actual  fact  from  the  radiation  of  the  heat  going  on 
in  the  skin  his  bodily  heat  is  actually  being  more  rapidly 
reduced. 


486  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

The  experiments  made  by  Blix  and  Goldscheider  proved 
the  existence  of  distinct  temperature  nerves,  and  showed 
that  there  are  on  the  body  warm  points  and  cold  points, 
and  that  whenever  a  warm  point  is  stimulated,  no  matter 
what  the  stimulus,  a  sensation  of  warmth  results,  while 
when  a  cold  point  is  stimulated,  even  though  it  be  with  a 
warm  object,  a  cold  sensation  results.  These  points  are  of 
course  normally  so  arranged  that  the  cold  points  are  more 
easily  affected  by  cold  and  the  warm  points  by  increase  of 
heat.  It  is  possible,  however,  to  use  electrical  stimuli  to 
affect  both  and  so  produce  in  one  class  cold  sensations  and 
in  the  other  warm  sensations  even  though  the  temperature 
in  the  meantime  may  have  varied  not  a  bit. 

These  temperature  nerves,  however,  do  not  end  in  special 
nerve  end-organs  but  in  networks  of  fibers  not  wholly  un- 
like the  dendrons  described  in  connection  with  the  central 
nervous  system.  These  warm  and  cold  points  are,  therefore, 
definite  anatomical  structures  and  it  is  possible  by  carefully 
exploring  the  skin  with  a  sharp-pointed  instrument  to  desig- 
nate these  points  and  to  make  an  exact  map  of  the  temper- 
ature topography. 

Finally  it  seems  probable  that  there  is  a  distinct  center 
for  cold  sensations  and  another  for  warm  sensations.  The 
probability  of  this  is  suggested  by  the  fact  that  an  arm  or 
limb,  when  subjected  to  pressure,  and  so  has  as  we  say 
4 'gone  to  sleep,"  is  still  able  to  perceive  warmth  but  is  in- 
sensible to  cold. 

THE  MUSCULAR  SENSE. 

When  the  muscles  are  called  into  action  one  is  clearly 
conscious  of  a  sensation  coming  apparently  from  these 
muscles  and  informing  one  of  their  extent  and  degree  of 
contraction.  It  is  perfectly  easy  for  an  individual  with 
closed  eyes  to  determine  exactly  the  position  and  move- 
ments of  his  muscles.  This  can  only  be  accomplished  by 
the  mind's  taking  note  of  the  sensory  impulses  that  come 
from  the  skin  of  the  part  moved  and  from  the  sensory 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE.  487 

nerves  distributed  among  the  ligaments  and  muscles  of  the 
same  part.  In  fact,  for  the  proper  manipulation  of  the 
muscles  we  are  largely  dependent  upon  the  impressions 
which  accompany  the  use  of  them.  An  individual  with 
sensation  lost  in  the  arm  is  unable  to  control  the  move- 
ments of  that  arm.  It  not  infrequently  happens  that  when 
an  arm  goes  to  sleep,  the  power  to  move  it  returns  before 
sensation  returns,  but  the  motions  so  accomplished  are 
of  the  most  clumsy  and  inaccurate  kind.  Experiments 
have  shown  that  horses  whose  trigeminal  nerve  (the  sensory 
nerve  to  the  head)  had  been  cut,  found  it  perfectly  impos- 
sible to  perform  even  such  simple  muscular  actions  as  the 
chewing  of  their  food.  A  frog  whose  spinal  sensory  nerves 
are  cut  finds  the  greatest  difficulty  in  the  performance  of 
his  otherwise  simplest  motions.  That  these  guiding  sensa- 
tions do  not  come  entirely  from  the  skin  is  shown  by  the 
fact  that  the  skin  may  be  entirely  removed  from  a  portion 
of  a  frog's  body  without  interfering  with  the  accuracy  of 
the  movement  of  his  muscles,  provided  the  sensory  nerves 
going  to  these  muscles  are  left  intact. 

In  the  chapter  on  the  histology  of  the  muscles  it  was 
pointed  out  that  muscles  themselves  are  not  sensitive  in  any 
way,  but  that  the  sensations  which  seem  to  come  from  the 
muscles  really  come  from  sensory  nerves  which  are  distrib- 
uted in  among  such  muscles.  Even  the  sense  of  fatigue 
of  muscles  has  such  an  origin. 

But  not  only  are  we  able  to  determine  the  amount  of 
motion,  but  it  is  possible  actually  to  measure  the  intensity 
of  the  muscle  contraction.  In  this  way  we  are  enabled  to 
form  judgments  as  to  the  weight  of  things.  A  weight  must 
change  from  at  least  one-fortieth  to  one-tenth  of  its  entire 
amount  in  order  to  perceive  a  difference.  No  doubt,  how- 
ever, the  ability  to  make  these  distinctions  varies  within  wide 
limits  and  is  largely  perfected  by  practice.  Individuals  who 
are  in  the  habit  of  weighing  things  become  finally  so  pro- 
ficient as  to  be  almost  trustworthy  in  that  matter.  There 
are  many  illusions  in  connection  with  the  matter  of  the 


488  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

judgment  of  weights.  Of  objects  that  have  the  same  weight 
those  that  are  larger  seem  lighter.  Again,  an  object  seems 
lighter  when  it  is  elevated  with  both  hands,  instead  of  one. 
No  doubt  we  judge  of  the  weight  of  objects  by  noticing  the 
amount  of  effort  necessary  to  bring  about  the  required 
motion.  Such  a  sensation  is  really  not  one  of  the  muscles, 
it  is  a  measurement  of  the  brain's  own  activity  in  the  inten- 
sity of  its  motor  impulses.  This  does  not  preclude  the  pos- 
sibility that  sensory  nerves  distributed  in  among  the  muscles 
may  take  part  in  giving  us  our  sensations  of  passive  move- 
ments. Not  only  are  we  able  to  perceive  motions  which  we 
voluntarily  make,  but  we  are  also  able  to  perceive  passive 
movements.  To  be  suddenly  moved  forward,  to  have  this 
motion  checked  or  to  be  turned  right  and  left,  or  to  have  the 
rapidity  of  the  motion  varied  is  at  once  a  matter  of  knowl- 
edge. It  seems  very  probable,  however,  that  this  knowl- 
edge of  passive  movements  is  in  no  sense  connected  with 
the  muscles,  or  even  due  to  the  inertia  of  the  body  or  its 
centrifugal  actions,  but  that  it  is  due  entirely,  or  at  least 
largely,  to  changes  which  are  occasioned  by  lymph  move- 
ments in  the  semi-circular  canals  of  the  ear,  in  connection 
with  which  a  detailed  explanation  of  this  matter  is  given. 

THE  SENSE  OF  TASTE. 

The  sense  of  taste  is  located  in  certain  parts  of  the  mucous 
membrane  of  the  mouth,  especially  on  the  mucous  membrane 
covering  the  tongue.  The  under  side  of  the  tongu,e  is  not 
sensitive  to  taste.  The  same  is  true  of  the  lips  and  gums 
and  the  cheek.  It  is  asserted,  however,  that  in  small  chil- 
dren these  parts  are  able  to  give  sensations  of  taste.  The 
exact  location  of  these  taste  areas  may  be  easily  established 
by  taking  a  sapid  powder  and  applying  it  point  for  point 
over  these  areas.  A  liquid  would  not  be  satisfactory  for 
this  purpose,  as  it  would  naturally  spread  to  the  neighboring 
areas.  The  sense  of  taste  may  also  be  anatomically  located 
by  the  presence  of  taste  bulbs.  These  taste  bulbs,  dis- 
covered by  Loven  and  Schwalbe  in  1867,  are  small  barrel- 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE. 


489 


shaped  bodies  filled    with   a  number  of   spindle-like   cells 
— hich   at  their  lower  extremities   are  connected  with  the 


Fig.  154. — SECTION  OF  PAPILLAE  FROM  TONGUE  OF  RABBIT,  SHOWING  POSITION  OF  TASTE- 
BUDS.     (After  Ranvier.) 
71,  nerve  cut  across;  v,  vein;  a,  gland;  g,  a  single  taste-bud. 

nerves  of  taste  and  at  their  upper  end  are  pointed  and  pro- 
ject to  the  exterior.     A  rather  rough  analogy  might  be  made 


\.  iit 

Fig.  155.— A  SINGLE  TASTE-BUD  MUCH  ENLARGED.     (After  Ranvier.) 
p,  the  open  pore;  *,  taste  cells;  m,  white  corpuscle  filled  with  granules-  r,  supporting: 
cell;  e,  ordinary  tongue  epithelium. 

by  imagining  an  ordinary  flour-barrel  filled  with  a  number 
of  sticks,  their  lower  ends  connected  with  wires  but   the 


490  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

upper  ends  of  the  sticks  somewhat  pointed  and  projecting 
above  the  body  of  the  barrel  free  into  the  exterior.  These 
taste  bulbs  are  most  plentiful  in  the  circular  depressions 
around  the  circumvallate  papillae  and  the  free  ends  of  the 
sensory  cells  project  into  this  groove .  They  are  also  found, 
although  not  so  plentifully,  on  the  fungiform  papillae  and 
even  on  the  soft  palate  and  epiglottis.  Their  preponderance 
towards  the  back  of  the  tongue  and  mouth  explains  the 
common  experience  that  the  sense  of  taste  is  most  acute  in 
those  regions.  In  fact,  the  sense  of  taste  is  rather  imperfect 
at  the  tip  of  the  tongue.  Yet  the  tip  seems  best  adapted  for 
sour  sensations  but  not  so  well  for  bitter  sensations.  The 
acuteness  of  the  sensation  in  the  back  of  the  mouth  possibly 
finds  its  explanation  in  the  tendency  which  this  gives  to  the 
animal  to  swallow  its  food. 

The  anatomical  arrangements  for  the  perception  of  taste 
at  the  tip  of  the  tongue  are  quite  different  from  the  taste 
bulbs,  the  sensory  nerves  here  ending  merely  in  fine  net- 
works of  fibrils.  In  the  description  of  the  cranial  nerves 
in  the  preceding  chapter  the  glossopharyngeal  was  pointed 
out  as  the  main  nerve  of  taste,  while  the  taste  sensations 
from  the  tip  of  the  tongue  were  ascribed  to  the  trigeminal. 
Some  physiologists  have  tried  to  make  the  difference  in  the 
nerves  going  to  these  areas  explain  the  difference  in  the 
acuteness  of  the  sensation,  but  more  recent  work  seems  to 
show  that  even  the  fibers  that  go  to  the  tip  of  the  tongue 
are  derived  from  the  glossopharyngeal  nerve  which  reach 
the  tip  of  the  tongue  along  the  trunk  of  the  trigeminal 
nerve. 

THE  NATURE  OF  A  TASTE  SENSATION. 

Gustatory  sensations  are  produced  by  substances,  either 
in  solution  when  introduced  into  the  mouth,  or  dissolved  by 
the  liquids  in  the  mouth.  Gases  dissolved  in  the  liquids  of 
the  mouth  may  thus  give  rise  to  actual  tastes.  In  what 
manner  these  substances  act  upon  the  nerve  endings  to 
produce  the  sensations  of  sweet,  or  sour,  or  salty,  etc.,  is 
entirely  unknown.  We  are  at  present  entirely  unable  to 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE.  491 

form  the  remotest  conception  of  it.  It  seems  probable 
though,  that  there  are  separate  nerves  for  the  separate 
tastes,  inasmuch  as  experiments  show  that  certain  papillae 
give  certain  tastes  only,  no  matter  how  stimulated,  while 
other  papillae  give  other  tastes.  Possibly  the  tips  of  the 
taste  cells  are  chemically  affected  by  sapid  substances,  cer- 
tain cells  readily  by  acids,  sour  substances,  others  by  sub- 
stances of  the  family  of  the  sugars,  producing  the  sweets, 
and  so  on.  These  impressions  are  then  conveyed  to  the 
brain,  and  in  the  brain  in  a  perfectly  subjective  way  what 
we  call  the  "  taste"  arises. 

That  there  is  a  large  subjective  element  in  taste  is  prob- 
able from  such  experiments  as  these:  Pure  distilled  water 
when  tasted  immediately  after  tasting  salty  water  tastes 
distinctly  sweet.  Still  more  remarkable  is  the  fact  that  a 
dilute  solution  of  sugar  becomes  distinctly  sweeter  to  the 
taste  when  a  little  bit  of  salt  has  been  added  to  it.  The 
intensity  of  the  sensation  depends  not  only  on  the  strength 
of  the  solution  to  be  tasted,  but  also  on  the  amount  of  taste 
area  in  the  mouth  in  contact  with  that  solution.  For  this 
reason  a  person  tasting  a  thing  tries  to  spread  it  out  as  much 
as  possible  over  his  sensory  area.  Rubbing  the  substance, 
pressing  it  against  tongue  or  palate  sharpens  the  taste,  no 
doubt  because  it  facilitates  the  introduction  of  the  sapid 
substance  into  the  depressions  around  the  circumvallate 
papillae  in  which  the  taste  buds  lie. 

Taste  sensations  are  frequently  confused  with  odors. 
Possibly  in  the  majority  of  instances  when  a  person  imagines 
he  is  tasting  something,  the  sensation  is  really  due  to  his 
olfactory  sense.  With  the  destruction  of  the  sensibility  of 
the  nose  goes  the  possibility  to  taste  such  apparently  sapid 
substances  as  coffee,  tea,  or  the  ordinary  flavors  of  fruits.  In 
fact,  the  number  of  tastes  are  limited  and  are  usually  classed 
in  four  kinds,  namely,  bitter,  sour,  sweet  and  salty.  In 
each  class  there  are,  of  course,  large  numbers  of  slightly 
varying  qualities. 


492 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


THE  SENSE  OF  SMELL. 

The  sense  of  smell  is  located  in  the  olfactory  region, 
which  includes  the  mucous  membrane  covering  the  folds  of 
the  ethmoid  bone,  and  the  turbinated  bones.  The  mucous 
membrane  in  these  parts  is  not  provided  with  cilia,  as  it  is 
in  the  regular  respiratory  tract  behind.  The  difficulty  of 
establishing  definite  end  organs  con- 
cerned in  the  sense  of  smell  is  even 
greater  than  in  those  of  taste,  and  the 
histology  of  the  mucous  membrane 
reveals  but  slightly  differentiated  struc- 
tures for  this  purpose.  There  are,  how- 
ever, in  the  epithelium  covering  this 
mucous  membrane  certain  more  slender 
cells  placed  in  between  the  ordinary 
epithelial  cells.  These  more  slender  or 
sensory  cells  are  connected  with  fibers 
from  the  olfactory  nerve  beneath,  are 
pointed  at  the  upper  end,  which  point 
projects  very  slightly  above  the  mucous 
membrane  into  the  nasal  cavity.  The 
statement  of  some  observers  that  in  the 
human  nose  these  sensory  cells  have 

Fig.  156.— OLFACTORY  CELLS,    little  hairs  or  cilia  at  their  end  is  prob- 
(After  M.  schuitze.)  aoly  not  true.     It  is  true,  however,  in 

1,  from  the  frog;  2,  human;  ,-t                              r     i   •    j  j                   1    't    • 

a.  ordinary  epUhelial  cells!  the     CaSG     °f     birds  aild     amphibians. 

6,  olfactory  cells;  c,  peri-  TllCSC    pOSSCSS     OU  the     ends    of     tllCSC 

pheral  process  prolonged                          ,11              •  11      i      •  ATA-I 

in  i  into  fine  hairs ;  a,  their    cells  rather  long  immovable  hairs .   The 
central   ends    connected    absence   of   such    hairs   in    man    may 

with  the  nerve.  •* 

account  for  his  bluntness  of  this  sense 

when  compared  with  the  intense  acuteness  of  that  of  some 
of  the  lower  animals.  The  tips  of  these  cells  projecting  into 
the  nasal  cavity  are  the  points  where  the  stimuli  that  pro- 
duce sensations  of  odor  affect  the  nerves.  It  is  at  once  ap- 
parent how  much  more  efficient  such  a  stimulus  would  be 
when  acting  upon  a  number  of  sensitive  protoplastic  hairs 
projecting  freely  above  the  surface  than  when  obliged  to  act 


TOUCH,  TEMPERATURE,  MUSCULAR  SENSE.  493 

on  a  relatively  blunt  end  only  slightly  raised  above  the  gen- 
eral epithelial  level. 

As  in  the  case  of  taste,  so  here  there  is  absolutely  no 
knowledge  at  present  as  to  the  exact  manner  in  which  the 
sensations  of  smell  are  produced.  Possibly  here,  too,  the 
subjective  element  plays  a  very  important  part,  for  it  not 
infrequently  happens  that  a  person  who  has  experienced  an 
exceedingly  unpleasant  odor  (such,  for  instance,  as  those 
associated  with  a  corpse)  will  have  this  odor  recur  after 
that  from  time  to  time  with  the  clearest  exactness,  although 
every  possibility  of  the  offending  gases  actually  having  af- 
fected the  nose  was  precluded.  Smell  sensations  are  oc- 
casioned by  the  introduction  of  gaseous  substances  only, 
but  the  intensity  of  the  sensation  depends  not  only  upon 
the  strength  of  the  gas,  but  also  upon  the  circumstance  that 
this  gas  must  stream  through  the  nose.  A  gas  allowed  to 
rest  in  the  nose  soon  ceases  to  affect  the  membrane.  For 
this  reason  the  air  is  always  sniffed  when  the  odor  of  any- 
thing is  to  be  detected. 

One  of  the  most  remarkable  things  about  the  sense  of 
smell  is  that  it  may  be  aroused  by  almost  inconceivably 
small  quantities  of  odorous  matter.  Musk,  for  instance, 
may  fill  large  spaces  with  its  odor  and  do  so  for  relatively 
long  times,  and  yet  not  lose  measurably  in  weight. 

A  further  interesting  fact  is  the  inability  we  have  of 
forming  anything  like  a  scale  of  odors,  or  even  our  inability 
to  divide  them  into  related  groups.  In  fact,  we  are  unable 
to  designate  them  with  definite  names,  but  apply  to  them 
the  names  of  the  objects  in  which  they  occur.  We  are  also 
further  entirely  unable  to  analyze  odors  into  their  compo- 
nents, a  thing  which  can  be  easily  done  in  the  matter  of 
colors  with  the  eye,  or  still  more  easily  with  sounds  in  the 
ear.  Even  when  one  nostril  is  filled  with  an  odor  of  one 
kind  and  the  other  nostril  with  a  different  odor,  the  two 
sensations  do  not  blend  at  all,  but  we  perceive  now  the  one, 
now  the  other,  depending  upon  the  relative  strength  or  sen- 
sitiveness of  the  two  nostrils. 


CHAPTER  XXII. 


THE   EAR. 

The  ear  is  an  apparatus  constructed  according  to  such 
physical  and  physiological  laws  as  will  enable  it  to  take 
cognizance  of  sound  vibrations.  The  adaptation  of  this  organ 
to  physical  sound  vibrations  is  one  of  remarkable  perfec- 
tion, exceeding,  possibly,  any  other  instrument  which  has 
to  do  with  the  manipulation  of  sound  waves.  Evidently, 
therefore,  it  is  necessary  in  order  to  understand  the  anatomy 
and  physiology  of  this  sense  organ  to  become  somewhat  ac- 
quainted with  the  physical  properties  of  sound  waves. 

THE  NATURE  OF  SOUND. 

Sound,  that  is,  sound  viewed  from  its  physical  stand- 
point, is  a  vibratory  motion.  The  body  moving  may  be 
either  gaseous,  liquid  or  solid.  The  vibration  is,  however, 
a  molar  vibration ;  the  mass  of  the  medium  in  question  must 
vibrate.  In  this  sound  differs  fundamentally  from  heat  and 
light,  which  are  also  forms  of  motion,  but  these  latter  are 
produced  by  the  molecular  motion  of  the  body  giving  out 
the  heat  or  light.  This  distinction  may  be  easily  made 
clear  by  imagining  a  bell  struck  first  with  a  hammer.  The 
blow  sets  in  vibration  the  entire  mass  of  the  bell.  This  vi- 
bration may  be  felt  with  the  finger,  and  a  small  object  sus- 
pended near  the  bell  is  violently  thrown  away  from  it  as 
soon  as  it  touches  it.  One  is  able  almost  to  see  the  oscil- 
lation of  the  whole  metal  backwards  and  forwards.  If  the 
bell  be  grasped  and  held  firmly  it  soon  ceases  to  vibrate  and 
the  sound  is  gone.  If,  on  the  other  hand,  such  a  bell 
should  be  placed  over  a  fire  it  would  gradually  become 
warmer  and  warmer,  and  if  the  heating  process  should  con- 
tinue, might  even  be  raised  to  a  red  heat,  and  so  produce 
light.  In  this  instance  it  is  not  the  whole  mass  of  the  bell 
(494) 


THK   EAR.  495 

moving  together,  but  it  is  a  molecular  motion  throughout 
its  substance.  Touched  with  an  object,  the  heat  vibrations 
do  not  cease,  and  a  small  piece  of  metal  placed  in  contact 
with  it  is  not  violently  thrown  off.  In  other  words,  sound 
is  a  vibratory  motion  of  the  mass  of  an  object,  heat  and 
light  of  its  component  molecules. 

THE  PRODUCTION  OF  SOUND. 

From  the  vibratory  nature  of  sound  it  follows  that 
sounds  may  be  produced  in  an  endless  variety  of  ways,  the 
requirement  in  each  case  being  simply  that  some  kind  of  a 
body  be  set  in  rapid  motion  and  that  this  motion  be  trans- 
mitted to  a  suitable  medium.  A  familiar  object  for  the  pro- 
duction of  sound  is  the  tuning-fork,  the  vibrations  of  which 
are  very  apparent  when  sounding;  in  the  case  of  the  organ 
the  metal  tongue  is  set  in  vibration  by  the  air  thrown  against 
it;  in  the  piano  it  is  the  strings  made  to  vibrate  by  the 
stroke  of  the  key  against  them,  while  in  wind-instruments 
the  air  itself  within  is  set  into  definite  oscillations. 

THE  RANGE  OF  THE  NUMBER  OF  VIBRATIONS  IN  THE  PRODUC- 
TION OF  SOUND. 

It  is  not  every  vibration  that  produces  a  sound.  It  is  not 
until  the  vibrations  reach  a  certain  frequency  that  they  be- 
come perceptible  to  the  ear.  The  minimum  number  of  vi- 
brations to  be  so  perceptible  varies  a  little  for  different  ears, 
but  is  in  the  neighborhood  of  sixteen  per  second.  A  string 
vibrating  fewer  times  than  sixteen  per  second  produces  no 
perceptible  sound,  although  its  vibrations  may  be  distinctly 
visible  to  the  eye.  Vibrations  above  this  lower  limit  are 
audible.  There  is,  however,  an  upper  limit  beyond  which 
the  ear  is  not  able  to  go.  This  upper  limit  also  varies  for 
different  ears,  but  seems  to  be  in  the  neighborhood  of  60,- 
000  vibrations  to  the  second.  These  limits  between  which 
the  human  ear  is  able  to  appreciate  sounds  comprise  a  range 
of  about  thirteen  octaves.  A  high-grade  piano  has  usually 
no  more  than  seven  octaves,  or  seven  and  one- third.  The 


496  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

superiority  of  the  ear  as  an  organ  for  catching  sound  several 
octaves  higher  and  lower  than  the  piano  is  at  once  apparent. 
The  compass  of  the  human  voice  is  about  three  octaves 
only.  Deep  F  of  the  bass  singer  has  about  87  vibrations, 
and  the  upper  G  of  the  soprano  about  775  vibrations  per 
second.  Voices  exceed  these  limits  only  in  very  excep- 
tional cases.  It  will  be  pointed  out  later  that  the  limits  of 
the  ear  are  not  limits  imposed  by  the  vibrations  themselves, 
but  that  these  limits  are  produced  in  consequence  of  the 
anatomy  of  the  ear,  the  basilar  membrane  having  an  extent 
of  about  thirteen  octaves  only.  It  is,  of  course,  entirely 
possible,  in  fact  probable,  that  an  anatomical  extension  of 
this  structure  in  the  ear  would  have  materially  increased  the 
range  of  the  musical  scale  which  might  be  perceived. 

THE  TRANSMISSION   OF   SOUND  IN  THE  AIR  AND  ITS  VELOCITY 

IN  THE  SAME. 

The  usual  medium  for  the  transmission  of  sound  is,  of 
course,  the  air.  Sound  is  unable  to  pass  through  a  vacuum. 
A  sounding  body  placed  under  a  bell  jar  of  an  air-pump  and 
the  air  then  exhausted,  cannot  be  heard,  no  matter  how 
violently  it  may  be  in  motion.  The  admission  of  air  into 
the  receiver,  and  so  the  formation  of  a  medium  around  it 
for  the  transmission  of  sound  at  once  makes  the  sound  loud 
and  clear.  Sound  waves  in  air  differ,  however,  in  form  from 
those  produced  by  the  tuning-fork  or  a  string.  The  sound 
waves  in  air  go  in  all  directions  from  the  sounding  point 
in  the  form  of  concentric  spheres,  somewhat  like  the  circles 
that  radiate  from  the  surface  of  a  body  of  water  from  the 
point  where  a  pebble  has  been  thrown  into  it.  In  the  case 
of  the  air,  these  waves  do  not  extend  in  the  form  of  circles 
but  in  the  form  of  spheres.  In  a  sound  wave  the  particles 
of  air  are  set  in  motion  in  such  a  way  that  they  produce 
spheres  of  condensed  air  and  rarefied  air,  and  it  is  these 
waves  of  condensation  and  rarefaction  that  are  transmitted, 
and,  of  course,  not  the  particles  of  air  themselves. 


THE   EAR.  497 

These  waves  go  with  a  velocity  which  can  be  readily 
determined.  That  sound  waves  are  much  slower  than  rays 
of  light  is  proved  by  the  experience  of  every  one  who  has 
seen  the  steam  of  the  whistle  of  an  approaching  train 
several  moments  before  he  hears  the  sound.  Or  he  may 
have  noticed  the  discharge  of  a  gun  or  the  flash  of  the 
lightning  before  he  hears  the  sounds  which  these  have  pro- 
duced. The  velocity  of  sound  vibrations  through  the  air 
depends  upon  the  density  of  the  air,  and  as  the  density  of 
the  air  depends  upon  the  temperature  it  is  usually  said  that 
the  velocity  of  a  sound  depends  upon  the  temperature  of 
the  medium.  At  the  temperature  of  freezing,  the  velocity  of 
sound  is  about  1,092  feet  per  second.  For  each  additional 
degree  of  centigrade  the  velocity  is  increased  about  two 
feet  per  second,  so  that  at  ordinary  mild  temperatures  the 
velocity  of  sound  in  air  is  not  far  from  1,120  feet  per 
second. 

REFLECTION  AND  REFRACTION  Ol  SOUND. 

Sound  being  a  vibratory  motion  it  is  subject  to  the  same 
laws  of  reflection  and  refraction  as  light.  A  sound  wave, 
for  instance,  striking  a  high  wall  or  precipice  is  reflected 
back  and  gives  rise  to  what  is  familiarly  known  as  the  echo. 
An  echo  in  sound  is,  therefore,  like  the  reflected  image  in 
a  mirror  in  the  case  of  light. 

But  not  only  may  sound  be  reflected  like  an  echo,  it  may 
be  refracted  like  light  through  lenses.  To  do  this  it  is  simply 
necessary  to  pass  the  sound  wave  through  a  denser  medium 
to  converge  it,  or  a  rarer  medium  to  diverge  it.  A  large 
rubber  bag  shaped  like  a  double  convex  lens  and  filled 
with  carbon  dioxide,  which  is  denser  than  air,  serves  as  a 
condensing  lens,  somewhat  like  glass  does  for  light.  Very 
seldom,  however,  are  sound  lenses  brought  into  use. 

A  familiar  result,  depending  upon  the  refraction  of  sound, 

is  produced  in  the  carrying  of  sound  by  the  winds.     It  is 

apparent  that  a  sound  is  much  plainer  when  the  wind  blows 

from  that  direction.     The  familiar  explanation  is,  of  course, 

32 


498  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

that  the  sound,  like  autumn  leaves,  has  been  blown  along 
by  the  wind.  This  is,  however,  a  mere  figure  of  speech. 
The  real  explanation  consists  in  the  fact  that  the  air  being 
blown  over  the  ground  and  meeting  with  resistance  there  is 
somewhat  condensed,  and  being  therefore  denser  on  the 
ground  than  it  is  further  up  where  there  is  no  resistance  to 
be  overcome,  the  sound  waves  are  deflected  towards  the 
ground,  by  this  denser  air  near  it  acting  like  an  ordinary 
lens.  In  this  way  much  of  the  sound  which  would  other- 
wise have  radiated  upwards  into  the  sky  is  refracted  to  the 
ground  and  so  the  perception  of  the  sound  made  more 
distinct.  The  analogy  in  the  case  of  light  occurs,  for 
instance,  at  the  rising  or  setting  of  the  sun  when  by  means 
of  the  refraction  of  the  atmosphere  the  sun  becomes  visible 
in  the  morning  really  before  it  comes  above  the  horizon, 
and  remains  visible  in  the  evening  some  time  after  it  has 
really  set,  due  to  the  fact  that  the  rays  of  light  which  would 
have  gone  off  into  space  are  by  the  atmosphere,  like  a  lens, 
bent  down  to  the  ground. 

THE  PHYSICAL  PEOPEETIES  OF  SOUND. 

1. — The  Intensity  or  Loudness.  Sounds  are  easily  dis- 
tinguished as  louder  or  softer,  and  this  distinction  in  loud- 
ness  is  described  as  the  intensity  of  the  sound.  This  in- 
tensity is  produced  by  the  intensity  of  the  vibration,  not  by 
the  frequency  or  number  of  vibrations.  This  must  remain 
the  same.  The  intensity  is  in  the  added  distance  through 
which  a  single  vibration  moves.  Thus,  in  the  case  of  a 
piano  string  if  it  be  struck  very  lightly,  it  vibrates  up  and 
down  through  a  very  small  distance,  if  it  be  struck  harder 
the  number  of  its  vibrations  is  not  increased,  but  the  string 
at  every  vibration  passes  through  a  greater  amplitude.  The 
explanation  of  intensity  may  be  easily  shown  to  the  eye  by 
the  pendulum.  One  can  easily  satisfy  himself  that  a  pendu- 
lum of  a  definite  length  makes  no  more  vibrations  in  a  given 
time  when  it  swings  out  far  to  the  right  and  left  at  each 
beat,  than  when  it  moves  but  little  out  of  its  vertical  posi- 


THE    EAR.  499 

tion.  No  matter  if  the  pendulum  of  a  large  clock  should 
move  through  an  arc  of  only  a  degree,  or  if  it  should  move 
through  an  arc  of  ninety  degrees  would  the  number  be 
changed,  but  it  is  of  course  evident  that  when  moving 
through  ninety  degrees  the  stroke  is  more  intense  than 
when  moving  through  one. 

If  a  tuning-fork  by  means  of  a  point  at  its  vibrating  ends 
could  be  allowed  to  trace  its  vibrations  on  a  revolving  drum 
the  intensity  of  the  sound  would  be  pictured  to  the  eye  by 
the  height  of  its  waves.  Intensity,  therefore,  is  usually 
explained  by  saying  that  it  is  that  property  of  a  sound  which 
depends  upon  the  amplitude  of  the  vibration.  Loudness  in 
sound  is  brightness  in  the  case  of  light. 

2. — Pitch.  We  readily  distinguish  sounds  as  higher  or 
lower,  and  we  speak  of  bass,  alto,  tenor  and  soprano  parts 
when  we  haVe  these  distinctions  in  mind  in  the  case  of 
singing.  This  highness  or  lowness,  or,  in  other  words,  the 
pitch  of  a  sound,  depends  upon  the  number  of  vibrations 
per  given  time,  of  which  the  sound  is  composed.  For  in- 
stance, sixteen,  or  more  generally  thirty-two  vibrations  per 
second  is  the  lowest  note  audible.  Middle  C  on  a  piano 
(French  pitch)  is  256  vibrations  per  second,  while  the 
upper  C  on  the  piano  has  over  2,000  vibrations  to  the 
second.  Pitch  is  expressed  in  another  way,  by  stating  that 
it  is  that  property  which  depends  upon  the  length  (not 
height  or  amplitude)  of  the  vibrations.  This  is  but  saying 
the  same  thing  in  another  form.  In  a  note  which  has  2,000 
vibrations  per  second  the  individual  waves  must  be  much 
shorter  than  in  a  note  that  has  but  32.  Just  as  in  a  chain 
having  100  links  to  the  foot,  the  individual  links  must  be 
much  shorter  than  a  chain  having  but  three  links  to  the 
foot.  Evidently  the  number  of  links  and  the  length  of  the 
individual  links  express  the  same  thing. 

Other  things  being  equal,  the  pitch  which  a  sounding 
body  will  produce  will  in  the  case  of  tuning-forks  or  vibrat- 
ing tongues  depend  upon  the  length  of  the  fork  or  tongue, 


500  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

the  pitch  being  higher  the  shorter  the  tongue.  In  the  case 
of  stringed  instruments  the  pitch  depends  upon  the  tight- 
ness with  which  the  string  is  stretched,  as  well  as  upon  the 
length  of  the  string.  In  the  tuning  of  a  violin,  for  instance, 
the  pitch  of  the  string  is  first  determined  by  the  tightness, 
and  after  that,  the  pitch  is  varied  by  shortening  the  length 
of  the  string  in  definite  proportions  by  placing  the  finger 
upon  the  same. 

3. — The  Quality  of  Sounds.  If  in  the  same  room  a 
note  should  be  sounded  by  each  of  a  half  dozen  instruments 
and  the  intensity  and  pitch  of  this  note  be  made  as  nearly 
the  same  as  possible,  the  ear  could  nevertheless  distinguish 
without  the  least  difficulty  between  the  sounds  produced  by 
the  violin,  the  piano,  the  horn,  the  organ,  or  the  human 
voice.  This  property  of  a  sound  by  means  of  which,  even 
when  pitch  and  intensity  are  the  same,  we  are  able  to  make 
these  very  definite  distinctions  is  called  the  quality  of  a 
sound.  There  are,  therefore,  as  many  different  qualities 
as  there  are  kinds  of  sounds.  Even  in  the  case  of  human 
beings  nearly  every  voice  has  its  own  quality  and  we  are 
able  to  recognize  an  individual  very  readily  by  his  voice. 
The  question  now  arises  what  the  physical  basis  for  the  dis- 
tinctions is. 

This  is  not  so  easily  made  clear  without  having  at  one's 
disposal  a  more  detailed  knowledge  of  harmonics  than  can 
be  assumed  in  this  discussion.  A  few  hints  or  suggestions, 
however,  as  to  its  explanation  may  be  helpful.  If  we  pic- 
ture to  ourselves  sound  waves  in  the  form  of  water  waves, 
it  is  evident  that  the  height  of  a  wave  represents  the  loud- 
ness  of  the  sound,  and  the  length  of  the  wave;  that  is,  the 
distance  from  the  crest  of  one  wave  to  the  crest  of  the  next 
one,  represents  the  pitch.  Now,  in  this  analogy  the  form 
of  the  wave  determines  the  quality  of  it.  Every  one  who 
has  been  at  the  lakeside  or  at  the  seashore,  or,  still  better, 
far  out  on  the  ocean,  must  have  been  struck  with  the  variety 
of  the  forms  of  waves  from  the  gentle,  undulating  swell  with 


THE    EAR.  501 

its  unbroken  glassy  surface  like  a  bulged  mirror,  to  the 
ploughed,  choppy  waves  of  the  English  Channel  or  Irish 
Sea.  He  has  noticed  how  the  surface  of  a  big  wave  is 
sometimes  covered  with  smaller  waves,  and  these  individual 
smaller  waves,  in  turn,  roughened  with  ridges  upon  them. 
It  is  not  difficult  to  see  how  the  form  of  a  wave  on  L,ake 
Michigan  might  differ  materially  from  the  form  of  a  wave 
on  another  body  of  water,  even  though  the  height  of  the 
waves  and  the  lengths  of  them  be  the  same.  This  differ- 
ence in  form  produces  the  quality  of  the  wave,  and  if  we 
had  special  senses  to  take  cognizance  of  such  water  waves, 
probably  one  would  have  no  difficulty  in  distinguishing  be- 
tween a  Lake  Michigan  wave  and  a  wave  from  the  Gulf  of 
Mexico,  or  another  from  the  middle  of  the  Atlantic. 

Leaving  this  analogy  and  defining  quality  in  the  terms 
of  sound  waves  it  is  this:  The  quality  of  the  sound  de- 
pends upon  the  number  of  secondary  waves  or  secondary 
sounds  which  are  super-imposed  upon  the  first  fundamental 
wave  or  sound.  This  was  conclusively  shown  by  the  ex- 
periments of  Helmholtz,  who,  by  means  of  properly  com- 
bined tuning-forks  was  actually  able  to  produce  the  qual- 
ities of  different  instruments.  To  use  the  analogy  of  light, 
quality  would  be  produced  by  taking  a  fundamental  color 
and  then  tinting  or  shading  that  color  within  narrow  limits 
by  the  addition  of  secondary  colors.  If,  therefore,  the 
quality  of  a  sound  is  due  to  its  compounding,  the  question 
naturally  arises,  what  would  be  the  quality  of  a  sound  per- 
fectly pure  without  the  admixture  of  secondary  waves. 
Such  sounds  are  produced  with  relative  purity  by  tuning- 
forks,  and  any  one  who  has  heard  a  high-grade  tuning-fork 
must  have  been  struck  by  its  mellow,  pure,  unmixed  qual- 
ity. If,  now,  to  such  a  fundamental  pure  sound  other 
tuning-forks  in  varying  strength  and  of  proper  pitch  be 
added  it  would  be  possible  to  reproduce  the  piano  note,  or 
tone  of  the  violin,  and  we  may  add  even  the  quality  of  the 
human  voice. 


502  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

HARMONY. 

A  succession  of  notes  varying  in  pitch  and  possibly 
other  properties  is  spoken  of  as  a  melody.  Melodies  need 
conform  to  no  especial  physical  rule,  but  are  almost  wholly 
determined  by  the  likes  or  dislikes  of  the  composer.  A 
pleasing  melody  to  one  is  not  necessarily  so  to  the  next. 
A  much  more  definite  arrangement  of  notes  occurs  in  har- 
mony. By  harmony  is  understood  the  consonance  of  two 
or  more  sounds.  Any  two  sounds  when  sounded  together 
are  by  no  means  necessarily  harmonious.  In  fact,  if  the 
sounds  were  selected  at  random  the  chances  would  be  very 
much  in  favor  of  their  proving  discordant  to  the  ear.  Har- 
mony is  dependent  upon  the  consonance  of  definite  specific 
sounds,  and  is,  at  least  with  the  majority  of  civilized  people, 
the  same  for  all  persons.  Every  normal  ear  hears  as  a  pleas- 
ant sound  the  consonance  of  a  note  and  its  octave.  Every 
player  on  the  piano  knows  that  C  and  G  produce  a  pleasant 
effect  when  sounded  together;  that  the  same  is  true  of  C 
and  E,  or  C  and  F,  confining  ourselves  in  this  illustration 
to  the  key  of  C.  C  and  B  produce  a  discord,  C  and  G^  are 
displeasing.  We  have  now  to  determine  what  physical 
property  it  is  that  determines  the  consonance  or  dissonance 
of  notes.  In  doing  so  it  is  necessary  to  bear  in  mind  that  a 
consonance  or  dissonance  is  first  determined  by  the  ear, 
apart  from  any  physical  considerations  of  the  sounds  in 
question.  A  person  who  knows  not  the  first  elements  of 
the  nature  of  sound  may  be  perfectly  able  and  is  perfectly 
able  to  feel  the  pleasurable  effects  of  certain  combinations 
of  sounds,  and  the  displeasing  effects  of  others.  The  proper 
chords  on  a  piano  or  in  an  orchestra  please  the  ears  of  the 
attuned  or  untuned  alike,  within  large  limits.  The  determi- 
nation of  the  physical  nature  of  harmony,  therefore,  consists 
merely  in  determining  the  relations  of  notes  which  have  been 
previously  selected  by  the  ear  as  harmonious. 

When,  now,  notes  which  are  harmonious  are  examined 
experimentally,  it  is  soon  established  that  the  physical  basis 
of  harmony  is  the  simple  matnematical  ratio  of  tJie  number 


THE   EAR.  503 

of  vibrations  of  the  component  sounds,  and  the  notes  are 
more  harmonious  as  the  mathematical  ratio  of  their  numbers 
of  vibrations  becomes  simpler  and  simpler.  Kvidently  the 
simplest  mathematical  ratio  is  1  to  1,  but  this,  of  course,  is 
unison.  The  next  simplest  mathematical  ratio  is  1  to  2. 
This  is  the  ratio  of  a  note  and  its  octave  \  that  is  to  say,  the 
octave  above  a  note  has  always  just  twice  as  many  vibra- 
tions as  the  note  itself.  If  middle  C,  therefore,  has  256,  the 
C  just  above  in  order  to  be  a  harmonious  octave  must  have 
512.  The  next  simplest  ratio  is  2  to  3.  This  ratio  is  found 
to  exist  between  a  note  and  the  perfect  fifth  of  that  note. 
Using  the  key  of  C  in  all  of  this,  it  is  the  combination  of  C 
and  G.  In  other  words,  for  every  two  vibrations  in  C,  G 
has  three,  or,  if  C  has  256  G  has  384  per  second.  The  next 
simplest  ratio  possible  is  3  to  4,  and  this  proportion  in  their 
vibrations  exists  between  C  and  F.  The  ratio  of  3  to  4  is 
thus  found  in  \\\o.  perfect  fourth.  The  ratio  of  4  to  5  is  the 
ratio  of  the  interval  between  C  and  E,  or  the  major  third. 
The  ratio  of  5  to  6,  6  to  7,  7  to  8,  8  to  9,  and  so  on,  are 
becoming  too  complicated  to  appear  harmonious  to  the  ear, 
and  we  feel  these  ratios  as  dissonances.  But  there  are  other 
simple  ratios;  3  to  5  is  a  simple  ratio,  and  this  is  a  ratio 
which  exists  between  C  and  A,  the  major  sixth.  The  ratio 
of  1  to  3  exists  between  C  and  G  in  the  next  octave,  while 
the  ratio  of  1  to  4  exists  between  C  and  the  upper  C  of  the 
next  octave. 

All  these  ratios  are  simple  ratios,  and  it  is  this  simplic- 
ity of  ratio,  which  is  simply  the  rhythm  of  their  vibrations 
expressed  mathematically,  that  produces  the  effect  of  har- 
mony upon  the  ear,  or  rather,  upon  the  mind. 

Complex  ratios  become  more  and  more  dissonant,  while  •* 
very  complex  ratios  finally  lose  all  harmonious  qualities  and 
tend  to  become  mere  noise.  If  the  question  be  asked  why 
notes  having  a  simple  ratio  to  each  other  appear  pleasant, 
or  harmonious,  the  answer  would  have  to  be  referred  out- 
side of  the  domain  of  physiology.  It  would  probably  be 
that  the  mind  naturally  and  for  inexplicable  reasons  likes 


504  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

definite  rhythms,  and  when  these  rhythms  are  easily  per- 
ceived; that  is,  are  mathematically  simple,  we  become  con- 
scious of  this  pleasure. 

Something  of  this  rhythm  appeals  to  the  eye.  Soldiers 
that  march  in  unison  present  a  pleasing  appearance.  A 
company  of  soldiers  composed  of  a  column  of  adults  and  a 
column  of  boys  marching  in  such  a  way  that  the  boys  would 
take  two  steps  while  the  adult  soldiers  took  one  step  would 
be  very  pleasing  to  the  eye.  The  interval  between  the  two 
columns  of  soldiers  would  really  be  an  octave.  We  can 
imagine  the  pleasing  effect  of  two  columns  marching  with 
such  regularity  that  for  every  two  steps  of  one  column  the 
other  should  take  three,  so  that  at  every  third  step  of  the 
second  column  all  of  the  soldiers  would  step  together. 
This  would  be  the  interval  of  2  to  3,  or  the  perfect  fifth. 
If,  finally,  all  mathematical  ratio  should  be  lost,  or  at  least 
become  very  complex,  we  would  no  longer  be  able  to  per- 
ceive any  rhythm  in  the  march,  and  the  column  now  would 
present  nothing  but  an  ordinary  crowd  rushing  in  confusion 
down  the  street.  This,  in  terms  of  sound,  is  mere  noise. 

In  the  building  of  a  musical  instrument,  therefore,  such, 
for  instance,  as  the  piano,  which  has  only  a  certain  number 
of  keys,  the  point  is  to  pick  out  those  notes  which  bear 
these  simple  ratios  and  omit  those  of  complex  ratios.  In 
this  way  there  is  produced  what  is  commonly  called  the 
scale,  consisting  of  eight  sounds.  The  vibrations  determin- 
ing these  notes  are  in  the  proportion  of  the  numbers  as  here 
given : 

CDEFGABC 
1,  9/s,  5A>  4/3,  3/2,  5/3,  15/s,  2. 

Cleared  of  fractions  these  proportions  may  be  expressed 
by  the  numbers, 

CDEFGABC 

24,  27,  30,  32,  36,  40,  45,  48. 

Thus  for  every  24  vibrations  of  C,  D  will  have  27,  A  40, 
and  the  upper  C  48,  etc. 


THE   EAR.  505 

Evidently  in  harmonics  we  are  not  concerned  with  the 
absolute  number  of  vibrations  but  only  with  the  relative. 
We  may  select  as  the  number  of  vibrations  of  our  funda- 
mental note  any  desired  number,  but  once  having  selected 
this  number  arbitrarily,  the  others  must  bear  these  definite 
ratios  to  it.  Thus,  the  French  standard  for  middle  C  is 
about  256;  the  C  of  the  Italian  opera  has  about  273,  while 
a  Musical  Congress  in  1834  at  Stuttgart  recommended  264 
as  a  standard  for  middle  C. 

Expressed  then  in  physical  terms,  a  harmonious  chord  on 
the  piano  is  a  combination  of  those  notes  which  bear  simple 
mathematical  ratios.  Taking  the  key  of  C,  such  a  chord 
would  be  composed  of  C-E-G  and  C,  or  C-F-A  and  C. 
These  are  the  ordinary  combinations.  Music  begins  to  be 
less  and  less  harmonious  as  the  ratios  become  more  com- 
plex, and  when  the  ratios  can  no  longer  be  perceived  at  all 
we  speak  of  sounds  as  mere  noise. 

SYMPATHETIC  VIBRATIONS. 

In  order  to  understand  the  manner  in  which  sounds  in 
the  air  finally  succeed  in  stimulating  the  internal  ear,  it  is 
necessary  to  understand  those  phenomena  of  vibrating 
bodies  designated  as  sympathetic  vibrations.  It  is  a  very 
general  experience,  when  singing  a  clear  note  near  some 
musical  instrument,  that  the  musical  instrument  will  catch 
up  that  tone  and  give  it  out  itself.  Sometimes  it  is  neces- 
sary to  remove  instruments  from  the  room  to  prevent  this 
interference.  Two  tuning-forks  tuned  alike  and  placed 
near  each  other  mutually  affect  each  other.  If  one  tuning- 
fork  be  sounded  the  vibrations  from  that  tuning-fork  will 
put  the  second  tuning-fork  in  vibration,  even  though  it  was 
perfectly  silent  to  begin  with,  and  the  second  tuning-fork 
may  go  on  sounding  after  the  first  one  has  been  mechanic- 
ally stopped.  In  a  music  store  where  numbers  of  instru- 
ments are  found  close  together  the  strong  sounding  of  a 
chord  on  one  piano  will  usually  set  similar  chords  vibrating 
in  the  other  pianos.  These  phenomena  are  produced  by 


506  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

having  the  strings  of  the  other  instruments  set  in  sympa- 
thetic vibration  by  the  sound  waves  emanating  from  the 
first. 

It  must  be  noted,  however,  that  one  note  will  produce  a 
sympathetic  vibration  of  another  only  when  the  two  notes 
so  produced  are  of  the  same  pitch,  or  bear  at  least  harmonic 
ratios  to  each  other.  To  sing  middle  C  into  a  piano  will 
set  in  vibration  the  string  of  middle  C,  not  that  of  D  or  B. 
To  understand  the  nature  of  sympathetic  vibrations  thor- 
oughly means  to  understand  the  manner  in  which  the  vibra- 
tions of  the  air  are  finally  transmitted  to  certain  chords  in 
the  ear. 

The  ear  has  a  piano-board  in  it  and  sounds  entering  it 
will  set  in  sympathetic  vibration  those  chords  which  are 
attuned  to  them. 

The  physical  explanation  of  these  sympathetic  vibrations 
is  simple.  One  can  easily  see  how  a  very  slight  wind  which 
would  come  in  regular  puffs  might  set  a  very  heavy  object 
swinging  after  a  while  if  these  puffs  should  occur  at  such 
regularities  that  they  would  always  strike  the  swinging 
object  just  at  the  proper  time.  When  the  waves  of  air  are 
synchronous  with  the  vibrations  of  the  body  a  slight  wave 
may  soon  put  in  motion  a  relatively  large  body.  If  we 
imagine  an  individual  sitting  in  a  swing  and  pushed  with 
but  one  finger,  but  the  push  administered  just  at  the  moment 
when  the  person  is  swinging  away  from  the  finger,  so  as  to 
get  the  full  benefit  of  the  push,  the  swing  may  be  soon  set 
in  motion  by  these  slight  finger  tips. 

So  with  the  vibrations  entering  the  ear  and  striking  a 
certain  string  whose  vibrations  are  exactly  attuned  to  it, 
they  finally  set  it  going  and  so  give  rise  to  the  production  of 
a  second  sound  which  is  the  counterpart  of  the  first. 

Having  in  this  preliminary  way  called  attention  to  some 
of  the  elementary  but  fundamental  properties  of  sound,  it 
is  possible  to  more  intelligently  understand  the  somewhat 
complicated  anatomy  of  the  auditory  apparatus  itself. 


THE    EAR.  507 

THE  ANATOMY  OF  THE  EAR. 

The  sense  of  hearing  has,  of  course,  from  time  imme- 
morial been  attributed  to  the  ear,  and  some  explanations  as 
to  the  manner  in  which  'hearing  occurred  were  advanced 
with  fair  accuracy  by  very  early  writers.  It  was,  however, 
reserved  for  the  last  decade  to  very  materially  advance  our 
knowledge.  It  was  impossible  to  understand  the  percep- 
tion of  musical  sounds  until  Corti,  in  1846,  worked  out 
carefully  the  anatomy  of  the  cochlea,  and  especially  the 
membranous  cochlea.  The  rods  of  Corti  bear  this  observer's 
name.  The  finer  anatomy  of  the  vestibule  and  the  ampullae 
was  understood  when  the  work  of  Max  Schultze  on  these 
structures  was  published  in  1850.  In  1842  the  physiologist 
Florens,  and  in  1869  Goltz  advanced  the  idea  that  the  semi- 
circular canals  were  not  directly  concerned  with  hearing, 
but  were  organs  of  equilibrium.  It  was,  however,  reserved 
for  Helmholtz  to  study  with  the  greatest  care  the  individual 
parts  of  the  ear,  and  to  him  we  are  indebted  largely  for  the 
present  conception  we  have  of  the  function  of  that  organ, 
as  well  as  for  the  theory  of  harmony  in  terms  of  which  the 
various  phenomena  of  musical  sounds  are  ext>lained. 

THE  EXTERNAL  EAR. 

The  external  ear  is  composed  of  the  outer  shell  of  the 
ear  called  the  concha,  and  the  opening  leading  to  the  tym- 
panic membrane  designated  as  the  auditory  meatus. 

1. — Concha.  The  concha  consists  mainly  of  elastic 
cartilage  and  serves  to  collect  the  sound  like  a  funnel  and 
direct  it  into  the  auditory  meatus.  As  such  a  collector  of 
sound  it  is,  however,  very  deficient  in  human  beings.  The 
external  ear  may  be  entirely  removed  without  apparently 
interfering  with  the  acuteness  of  hearing.  In  the  lower  ani- 
mals its  efficiency  as  a  collector  is  unquestioned.  In  these 
animals  it  is  relatively  much  greater,  is  more  definitely 
funnel-shaped,  and  is  movable  in  such  a  way  that  it  may  be 
placed  in  the  most  advantageous  position  in  gathering  the 
sound.  In  the  human  ear  it  has  lost  most  of  these  proper- 


508  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

ties  and  so  may  be  looked  upon,  physiologically  at  least,  as 
an  inherited  remnant  of  a  once  more  serviceable  structure. 


Fig.   156.— A  SEMI-DIAGRAMMATIC    SECTION    THROUGH  THE  RIGHT  EAR. 

A,  auditory  nerve;  S,  semicircular  canal;  <?,  meatus;  M,  concha;  T,  tympanic  mem- 
brane; P,  middle  ear;  R,  Eustachian  tube;  S,  cochlea;  Vt,  scala  vestibuli;  Pt,  scala  tym- 
pani;  r,  round  foramen;  o,  oval  foramen.  (The  membranous  cochlea  is  not  shown.) 

2. — Meatus.  Through  the  auditory  meatus  the  sound 
waves  are  led  to  the  tympanic  membrane.  The  meatus  is 
lined  with  skin,  in  which  are  imbedded  numerous  wax 
glands,  the  secretion  of  which  serves  to  keep  the  wall  of  the 
passage,  as  well  as  the  tympanic  membrane  at  its  end,  in  a 
pliable  condition.  The  presence  of  relatively  large  hairs  in 
it  serves  mechanical  purposes  only,  in  preventing  access  to 
foreign  bodies.  It  was  held  by  some  physiologists  that  the 
external'  auditory  meatus  serves  as  a  resonance  cavity  for  the 
sounds,  but  owing  to  its  small  size  this  physical  effect  is  very 
trifling,  and  what  resonance  there  is  in  connection  with  the 
ear  belongs  probably  entirely  to  the  middle  ear. 

As  the  efficiency  of  the  eye  may  be  materially  increased 
by  the  addition  of  optical  instruments,  so  it  is  possible  to 
magnify  the  perceptive  capacity  of  the  auditory  meatus  by 
special  instruments,  such  as  ear- trumpets  and  the  profes- 
sional stethoscope. 


THE    EAR.  509 

THE  MIDDLE  EAR. 

The  middle  ear  or  tympanum  consists  of  a  small  cavity 
lying  between  the  external  auditory  meatus  and  the  inner 
ear.  Its  size  in  man  is  from  three-quarters  of  an  inch  in  its 
widest  dimension  to  about  a  half  inch  in  the  direction  at 
right  angles  to  this.  It  is,  therefore,  although  a  small 
opening  almost  as  large  as  the  entire  internal  ear,  or  in 
space  equal  to  the  external  auditory  meatus. 

1. — Eustachian  Tube.  This  cavity  is  filled  with  air 
which  is  able  to  reach  it  through  the  Eustachian  tube. 
This  tube  runs  from  the  middle  ear  and  opens  into  the  back 
part  of  the  mouth.  By  means  of  this  tube  the  pressure  of 
air  in  the  tympanum  is  kept  the  same  as  that  of  the  sur- 
rounding atmosphere,  and  so  barometric  changes  in  it  do 
not  exert  their  effect  upon  the  tympanic  membrane  as 
would  otherwise  happen.  Through  this  Eustachian  tube 
the  mucous  membrane  of  the  middle  ear  is  a  continuation 
of  the  mucous  membrane  of  the  mouth,  a  condition  which 
unfortunately  makes  possible  the  extension  of  an  inflam: 
mation  into  the  middle  ear  from  the  mouth,  such  as  occurs 
in  some  forms  of  catarrh.  An  inflammation  of  the  middle 
ear  and  Eustachian  tube  soon  causes  the  closing  of  the 
Eustachian  tube  by  its  swelling,  and  thus  the  only  exit 
for  the  matter  which  may  be  produced  is  by  rupturing  the 
tympanic  membrane  and  escaping  through  the  auditory 
meatus.  Such  a  result  is  usually  designated  as  a  gathering 
in  the  head.  The  Eustachian  tube  is  usually  closed,  the 
two  walls  of  it  are  pressed  together  and  separate  regularly 
only  during  the  process  of  swallowing.  The  explanation 
of  the  regularly  closed  condition  is  found  in  the  fact  that 
such  a  closing  prevents  the  sound  from  entering  the  middle 
ear  by  that  avenue,  and  so  to  some  extent  interfering  with 
the  sound  reaching  it  regularly,  and,  secondly,  that  it  pre- 
vents the  sounds  produced  in  the  mouth  (the  voice) ,  from 
reaching  the  ear  with  the  force  that  they  would  do  if  this 
canal  were  open. 


510  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

2. — Tympanic  Membrane.  The  tympanum  or  middle 
ear  is  separated  from  the  auditory  meatus  by  a  delicate 
membrane  called  the  tympanic  membrane.  This  mem- 
brane consists  of  three  coats :  a  connective  tissue  membrane 
covered  on  the  outside  with  the  skin  of  the  auditory  meatus 
and  on  the  inside  with  the  mucous  membrane  of  the  middle 
ear.  This  tympanic  membrane  is  set  somewhat  diagonally 
across  the  end  of  the  meatus  and  its  surface  toward  the 
meatus  is  concave.  This  concavity  is  produced  by  the 
circumstance  that  the  malleus  is  by  its  handle  firmly  at- 
tached at  the  middle  of  this  membrane  and  tends  to  pull  it 
inward.  Its  concavity  towards  the  exterior  possibly  serves 
to  gather  up  the  sound  waves  and  center  them  on  the  spot 
where  the  malleus  is  attached. 

The  tympanic  membrane  is  affected  by  sound  waves  in 
such  a  way  that  it  is  set  into  vibrations  corresponding  pre- 
cisely with  the  vibrations  of  the  entering  sounds.  This 
function  of  the  membrane  is  well  shown  in  the  telephone. 
The  box  into  which  one  speaks  has  stretched  across  it  at  its 
base,  just  in  front  of  the  electric  magnet  a  delicate  metal 
diaphragm.  Against  this  diaphragm  or  tympanic  membrane, 
so  to  speak,  the  voice  is  thrown  and  sets  it  into  vibrations 
which  correspond  exactly  to  the  vibrations  of  the  air  affect- 
ing it.  Such  a  telephone  membrane  is  able  to  catch  the 
vibrations  of  a  high  note  as  well  as  a  low  note.  It  is,  in 
fact,  able  to  transmit  to  the  magnet  back  of  it  all  the  vibra- 
tions which  strike  it. 

Such  is  almost  exactly  the  case  with  the  tympanic  mem- 
brane. This  membrane  has,  however,  one  or  two  arrange- 
ments by  means  of  which  it  can  adjust  itself  to  sounds. 
Attached  to  the  malleus  there  is  a  muscle  called  the  tensor 
tympani,  by  the  contraction  of  which  the  tympanic  mem- 
brane is  pulled  further  inward,  thereby  made  more  concave 
and  of  course  becoming  more  stretched.  This  probably 
helps  in  the  perception  of  high  sounds.  It  is  further  pos- 
sible that  this  tensor  tympani  is  brought  into  play  when  we 
listen  attentively  for  some  time  to  a  definite  sound.  One 


THE    EAR.  511 

can  readily  understand  that  a  tightly  stretched  membrane 
is  more  serviceable  for  collecting  sounds,  especially  high 
sounds,  than  a  less  taut  one. 

There  seems  little  reason,  though,  for  attributing  very 
much  to  this  muscle.  The  membrane  in  the  telephone  is 
able  to  catch  the  widest  range  of  tones  without  its  stretch 
being  varied,  and  so  there  seems  no  difficulty  in  attributing 
the  same  physical  possibilities  to  its  analogue  in  the  ear. 

3. — The  Bones  of  the  Ear.  The  vibrations  of  this  tym- 
panic membrane  must  now  be  carried  across  the  middle  ear 
to  the  internal  ear  where  the  real  sensory  apparatus  of  the 
ear  lies.  This  is  done  by  a  series  of  three  small  bores, 
known  as  the  hammer,  anvil  and  stirrup;  or,  using  their 
Ivatin  equivalents,  the  malleus,  the  incus  and  the  stapes. 
These  three  bones  really  represent  four  bones ;  as  the  incus 
consists  really  of  two  separate  bones,  the  incus  proper  and 
the  small,  round  orbiczdar  bone  which  finally  grows  to  it 
and  which  serves  to  attach  the  incus  to  the  stapes.  These 
three  bones  are  arranged  in  such  a  way  as  to  form  a  system 
of  levers,  by  means  of  which  the  vibrations  of  the  tympanic 
membrane  are  carried  across  the  middle  ear  and  with 
mathematical  precision  transmitted  to  the  inner  ear  through 
the  oval  foramen. 

A  somewhat  ingenious  arrangement  is  found  in  the  ar- 
ticulation of  the  malleus  and  the  incus.  These  at  their 
point  of  contact  fit  into  each  other  in  a  kind  of  dovetail 
fashion,  owing  to  the  presence  of  peculiar  interlocking 
teeth,  so  arranged,  however,  that  the  least  motion  of  the 
malleus  inwards  is  at  once  by  means  of  these  cog-like  teeth 
transmitted  to  the  incus  and  so  to  the  internal  ear.  A 
violent  motion,  however,  of  the  malleus  outward  does  not 
draw  the  incus  with  it.  In  this  way  there  is  prevented  the 
possibility  of  having  the  stirrup  pulled  out  of  the  oval  fora- 
men in  case  the  tympanic  membrane  should  be  suddenly 
and  forcibly  pressed  outward.  The  value  of  this  arrange- 
ment is  evident  when  we  remember  how  easily  one  might 


512  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

in  certain  forms  of  blowing,  force  the  air  through  the  Eu- 
stachian  tube  into  the  middle  ear,  and  thereby  push  out  the 


Fig.  157.— THE  BONES  OF  THE  MIDDLE  EAR,  WITH  ARROWS  INDICATING  THE  DIRECTION 

OF  MOVEMENT   OF  EACH   BONE  IN   THIS   SERIES   OF  LEVERS.      a,  am,  FULCRUM  POINTS. 

tympanic  membrane,  the  result  of  which  would  be  to  pull 
its  chain  of  bones  with  it,  even  at  the  risk  of  pulling  the 
stapes  entirely  out  of  its  moorings.  But  this  is  prevented 
by  the  arrangement  of  the  teeth  between  the  incus  and 
malleus  in  the  manner  just  stated,  so  that  while  a  motion 
inward  is  at  once  communicated  to  the  incus,  a  motion  out- 
ward affects  the  malleus  alone. 

The  exact  manner  in  which  these  bones  work  may  be 
easily  understood  from  the  accompanying  diagram,  in  which 
the  direction  of  motion  of  the  various  parts  is  indicated  by 
arrows.  It  will  be  noticed  that  the  malleus  moves  like  a 
lever  of  the  first  class,  its  fulcrum  being  near  its  middle 
at  the  point  where  it  is  fastened  by  means  of  the  ligaments 
to  the  wall  of  the  middle  ear. 

4. — The  Cavity  of  the  Middle  Ear.  The  function  of 
the  middle  ear  is  its  ability  to  act  as  a  resonance  cavity. 
But  for  this  fact  the  tympanic  membrane  might  have  been 
stretched  across  the  oval  foramen  at  once.  Sounds  are  ma- 
terially strengthened  when  brought  near  resonators.  The 
note  of  a  violin  is  to  a  very  large  extent  made  possible  by 
the  resonance  of  the  violin  frame  beneath  the  string.  It  is 
the  piano-board  almost  as  much  as  the  string  that  gives  the 
tone,  while  in  the  case  of  a  horn,  tones  would  be  impossible 
without  the  resonance  cavities  in  the  horn.  A  tuning-fork 


THE    EAR.  513 

sounded  by  itself  sounds  but  feebly,  but  placed  on  a  reso- 
nance box  of  the  proper  kind  it  is  increased  many-fold 
in  strength.  So,  too,  in  the  middle  ear  the  air  serves  such 
resonance  purposes.  Even  the  bone  surrounding  the  mid- 
dle ear  is  very  porous,  indeed,  and  it  is  not  impossible  that 
this  porosity  may  help  to  increase  still  further  this  reso- 
nance function. 

It  will  be  noticed  that  both  external  and  middle  ears 
were  purely  physical  arrangements  to  transmit  the  sound 
in  a  definite  way  to  the  internal  ear  where  the  real  act  of 
perception  occurs. 

THE  INTERNAL  EAR. 

The  real  sensory  internal  ear,  that  part  to  which  the 
auditory  nerve  is  distributed,  is  a  series  of  membranous 
canals  and  sacs  which  lie  in  corresponding  openings  in 
the  petrous  portion  of  the  temporal  bone.  We  have  there- 
fore to  do  first  with  the  bony  internal  ear,  by  which  is 
meant  nothing  more  than  that  system  of  spaces  in  the 
bone  in  which  the  membranous  or  sensory  ear  is  located. 
The  membranous  ear  does  not,  however,  occupy  all  of  the 
space  of  the  bony  ear,  but  floats  in  the  perilymph,  a  liquid 
which  fills  this  space. 

The  bony  ear  shows  three  well-marked  divisions  which 
appear  also  in  the  membranous  ear.  First,  the  vestibule; 
second,  the  semi-circular  canals;  third,  the  cochlea.  These 
three  portions  are  continuous  so  that  the  perilymph  in  the 
vestibule  might,  if  it  could  be  set  in  motion,  pass  through 
any  one  of  the  semicircular  canals  or  flow  up  the  windings 
of  the  cochlea. 

1. —  Vestibule.  The  vestibule  has  a  large  opening  com- 
municating with  the  middle  ear.  This  is  the  foramen 
ovale  into  which  the  end  of  the  stapes  fits.  It  is  evident, 
therefore,  that  the  vibrations  communicated  to  the  internal 
ear  by  the  stapes  reach  the  perilymph  of  the  vestibule. 

Connected  with  the  vestibule  towards  the  back  and 
slightly  above  are  three  semicircular  canals  arranged  like 
33 


514  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

the  three  diameters  of  a  cube.     One  is  vertical,  the  other 
vertical  at  right  angles  to  this,  and  the  third  horizontal. 


Fig.  158. — RIGHT  BONY  LABYRINTH  SEEN  FROM  THE  OUTER  SIDE.  (After  Sbmmerring.) 
The  smaller  figure  below  gives  the  actual  size.  1,  vestibule;  2,  foramen  ovale;  3,  4,  5, 
semicircular  canals;  6,  7,  8,  cochlea;  9,  foramen  rotundum.  (The  immediate  walls  of  the 
bony  labyrinth  are  denser  than  the  outer  portions,  and  the  view  above  results  when  the 
softer  bone  has  been,  piece  by  piece,  picked  away.) 

2. — Cochlea.  At  the  forward  end  of  the  vestibule  this 
space  communicates  with  the  cochlea.  This  structure, 
named  from  its  resemblance  to  a  snail  shell,  has  two  and 
one-half  windings.  It  is  a  tube  coiled  up  like  a  snail  shell, 
possibly  merely  to  save  space.  Drawn  out  it  would  be  a 
straight  tube  not  unlike  a  small  dinner-horn. 

The  cavity  of  this  coiled  tube  is,  however,  divided  into 
an  upper  and  a  lower  chamber,  the  upper  one  being  called 
the  scala  vestibuli,  the  lower  the  scala  tympani.  The  divi- 
sion is  formed  partly  by  a  partition  of  bone  called  the  lamina 
spiralis  and  partly  by  a  thin  membrane  called  the  basilar 
membrane.  These  two  chambers  are  so  arranged  that  the 
scala  vcstibtili  is  a  direct  continuation  of  the  cavity  of  the 
vestibule. 

The  scala  vestibuli  runs  to  the  top  of  the  cochlea,  and 
at  the  top,  on  account  of  the  absence  of  the  partition  at 
this  point,  it  communicates  with  the  scala  tympani,  while 
the  scala  tympani  at  its  lower  end  communicates  with  the 
middle  ear  through  the  round  foramen.  Both  these  scalac 
are  filled  with  perilymph. 


THE   EAR.  515 

Let  us  imagine  the  possibility  of  an  object  moving  around 
in  the  perilymph.  Such  an  object  starting  in  the  vestibule 
might  move  backwards  and  pass  through  any  one  of  the 
three  semicircular  canals,  going  up  one  and  down  the  other. 
Afterwards  it  might  move  back  through  the  perilymph  of 
the  vestibule  and  go  into  the  scala  vestibuli.  This  it  might 
ascend,  by  taking  the  two  and  one-half  turns  of  the  cochlea, 
to  the  very  summit.  The  continuity  of  the  partition  all 
along  the  cochlea  formed  by  the  lamina  spiralis  and  the 
basilar  membrane  would  make  it  impossible  to  pass  into  the 
scala  tympani.  But  at  the  very  top  this  partition  is  absent, 
and  the  scala  vestibuli  connects  with  the  scala  tympani. 
The  imaginary  object  might,  therefore,  pass  into  the  scala 
tympani,  descend  through  two  and  one-half  turns  the  scala 
tympani,  and  finally  reach  the  round  foramen  which  leads 
into  the  middle  ear.  There  is,  of  course,  stretched  across 
this  foramen  a  delicate  membrane  which  prevents  the  peri- 
lymph from  flowing  into  the  middle  ear.  If  the  imaginary 
object  at  the  round  foramen  were  to  return  to  the  vestibule 
it  could  do  so  only  by  re-ascending  the  scala  tympani  to 
the  top  of  the  cochlea,  passing  into  the  scala  vestibuli  and 
descending  the  scala  vestibuli  to  the  vestibule. 

3. —  The  Path  of  a  Sound  Wave  Through  the  Inner  Ear. 
Perhaps  it  will  be  helpful  in  understanding  the  reason  for 
this  arrangement  to  follow  a  sound  wave  after  it  has  reached 
the  oval  foramen  by  way  of  the  stapes. 

The  wave  is  (1)  transmitted  by  the  movements  of  the 
stapes  to  the  perilymph  of  the  vestibule.  In  the  perilymph 
the  vibrations  run  in  every  direction,  but,  as  we  shall  find 
that  the  perception  of  sound  occurs  in  the  cochlea,  we  are 
interested  only  with  those  vibrations  which  reach  it.  The 
vibrations  which  reach  the  semicircular  canals  do  not,  as 
far  as  we  know,  figure  in  any  way  in  hearing  and  so  may 
be  disregarded.  From  the  vestibule  the  sound  goes,  (2) 
up  the  continuation  of  the  perilymph  through  the  scala 
vestibuli  of  the  cochlea  to  the  top  of  same.  (3)  At  the  top 


516  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

where  the  partition  is  missing  the  sound  wave  reaches  the 
scala  tympani  and,  (4)  then  descends  the  scala  tympani  to 
the  round  foramen  by  the  movements  of  the  membrane  of 
which  it  is  (5)  finally  led  back  into  the  middle  ear  and 
so  lost.  A  sound  wave  does  not,  therefore,  go  into  the 
internal  ear  to  be  there  lost,  but  is  passed  through  the  same 
in  such  a  way,  that  the  reflection  of  a  sound  wave  back- 
wards in  the  form  of  an  echo  is  prevented.  It  is  evident 
that  if  one  vibration  after  another  should  run  into  the  peri- 
lymph,  that  unless  these  vibrations  could  pass  out  again 
they  would  be  reflected  back,  and  meeting  new  vibrations 
entering  produce  a  confusion  that  would  preclude  the  pos- 
sibility of  distinctly  hearing.  We  shall  see  that  the  ear 
perceives  these  waves  as  they  pass  unhindered  by. 

Having  examined  the  bony  labyrinth  it  is  possible  to 
place  in  it  more  intelligently  the  real  sensory  or  membran- 
ous part. 

THE  MEMBRANOUS  EAR. 

In  the  vestibule  the  membranous  ear  consists  of  two 
sac-like  expansions  connected  by  means  of  a  narrow  bridge. 
The  sac  nearest  the  cochlea  is  called  the  sacculus,  the  one 
nearest  the  semicircular  canals  the  utriculus.  The  sacculus 
and  utriculus  float  in  the  perilymph.  They  are  hollow  struc- 
tures and  are  filled  with  a  liquid  called  the  endolymph.  As 
the  membranous  ear  is  an  entirely  closed  structure  the  peri- 
lymph  around  it  and  the  endolymph  within  it  are  in  no  place 
in  direct  communication. 

Arising  from  the  utriculus  are  three  membranous  semi- 
circular canals  which  pass  through  the  bony  semicircular 
canals,  occupying,  however,  only  a  relatively  small  part  of 
the  space  of  these.  On  one  limb  of  each  semicircular  canal 
near  to  where  it  arises  from  the  utriculus  there  is  a  marked 
expansion  called  an  ampulla.  This  dilatation  is  shared  by 
the  bony  canal  as  well. 

Connected  with  the  sacculus  there  is  a  small  tube  which 
leads  into  the  cochlea  and  extends  to  the  very  top.  This  is 
the  membranous  cochlea.  It  is  really  nothing  but  a  tube- 


THE   EAR. 


517 


like  extension  of  the  sacculus  coiled  two  and  one-half  times, 
and  in  the  bony  cochlea  lies  just  above  the  basilar  mem- 
brane. It  is  in  the  cochlea  triangular  in  form,  the  basilar 


s.e. 


Fig.   159.— THE  MEMBRANOUS  INNER  EAR. 

u,  utriculus  with  contained  macula  acustica;  s,  sacculus  with  contained  macula  acus- 
tica;  *.  s.  c,  superior,  p.  s.  c,  posterior,  e.  8.  c,  external  semicircular  canal,  the  crista  acus- 
tica being  indicated  in  each  ampulla;  c,  r,  canalis  reunieus,  connecting  the  membranous 
cochlea  with  the  sacculus ;  c,  c,  the  membranous  cochlea ;  s,  e,  the  ductus  endolymphaticus. 
This  duct  serves  to  connect  the  utriculus  and  the  sacculus,  and  ends  blind  below  in  the 
sac-like  enlargement  called  the  saccus  endolymphaticus. 

membrane  being  the  floor  of  it,  and  the  membrane  of  Reiss- 
ner  being  one  of  the  sides.  It  lies,  therefore,  between  the 
scala  tympani  and  the  scala  vestibuli,  and  for  that  reason  is 
frequently  called  the  scala  media.  The  scala  media  is  filled 


Fig.  160. — SECTION  OF  THE  LEFT  COCHLEA  OF  A  CHILD,  six  TIMES  NATURAL  SIZE,  SHOW- 
ING   THE    MODIOLUS,    THE    SCALA    TYMPANI,    SCALA    VESTIBULI,    AND    SCALA    MEDIA. 

(After  Reichert.) 

with  endolymph,  which  is  in  direct  continuity  with  the  endo- 
lymph  in  the  sacculus,  but  is  entirely  shut  off  from  the  peri- 
lymph  around  it.  In  this  membranous  cochlea  we  find  the 


518  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

organs  of  Corti  and  the  endings  of  the  nerves  and  so  the 
points  in  the  ear  where  physical  vibrations  give  rise  to 
nervous  sensations. 

THE  HISTOLOGY  OF  THE  MEMBRANOUS  LABYRINTH. 

1. — Sacculus  and  Utriciilus.  Both  sacculus  and  utricu- 
his  are  hollow,  sac-like  structures  rilled  with  endolymph. 
There  is  found,  however,  at  those  points  on  the  sacculus 
and  utriculus  where  the  auditory  nerve  enters  them  a  small 
projection  called  the  maciila  acustica.  This  macula  acustica 
is  a  kind  of  a  projection  inward,  on  the  top  of  which  there 
are  the  auditory  hairs  projecting  into  the  endolymph.  These 
auditory  hairs  are  really  continuations  of  the  auditory  cells 
which  are  found  in  the  macula  acustica  and  which  are  con- 
nected at  their  bases  directly  with  the  auditory  nerve. 

In  the  mucilaginous  matrix  between  these  auditory  cells 
there  are  imbedded  very  small  stones  called  the  otoliths. 
These  otoliths  are  composed  of  calcium  carbonate  and  their 
function  is  probably  to  help  stimulate  the  nerve  cells  by 
their  inertia  when  set  in  motion  by  the  endolymph.  The 
otoliths  in  man  are  only  microscopic  crystals,  but  in  the 
fishes  and  some  of  the  invertebrates  they  become  quite  large, 
a  half  inch  or  more  in  diameter. 

2. — Semicircular  Canals.  Connected  with  the  utriculus 
are  three  semicircular  canals  each  of  which  possesses  on 
one  of  its  limbs  an  enlargement  known  as  the  ampulla.  A 
cross-section  of  such  an  ampulla  shows,  projecting  into  the 
interior  of  it  the  crista  acustica.  This  projects  inward 
relatively  much  further  than  the  macula  acustica  just  re- 
ferred to. 

An  epithelium  of  auditory  cells  connected  with  the  audi- 
tory nerve  covers  the  crista.  Delicate  hairs  from  these  pro- 
ject into  the  surrounding  endolymph.  At  other  portions  of 
the  semicircular  canal  it  is  a  smooth  tube  lined  with  ordi- 
nary epithelium,  and  has  at  these  portions  probably  no  definite 
sensory  functions. 


THE    EAR.  519 

THE  MINUTE  STRUCTURE  OF  THE  MEMBRANOUS  COCHLEA. 

The  position  of  the  membranous  cochlea  between  the 
scala  vestibuli  and  scala  tympani  has  been  referred  to.  Its 
shape  as  a  triangular  tube  running  from  the  sacculus  to 
the  top  of  the  cochlea  has  been  stated.  Speaking  approxi- 
mately its  boundaries  are  as  follows:  The  upper  side  formed 
by  the  membrane  of  Reissner  separates  it  from  the  scala 
vestibuli ;  the  lower  side  is  formed  by  the  basilar  membrane 
and  a  part  of  the  lamina  spiralis,  these  two  separating  it 
from  the  scala  tympani.  Its  outer  wall  is  formed  by  the 
wall  of  the  bony  cochlea  itself. 

1. — Basilar  Membrane.  The  essential  structure  in  this 
membranous  cochlea  is  the  basilar  membrane.  This,  al- 
though called  a  membrane,  really  consists  of  a  number  of 
strings  of  varying  length  stretched  from  the  edge  of  the 
lamina  spiralis  to  the  outer  wall.  These  strings  are  shortest 
at  the  base  of  the  cochlea  and  become  gradually  longer 
towards  the  top.  If  this  basilar  membrane  were  removed 
from  the  cochlea  and  straightened  out  it  would  have  the 
appearance  given  in  Figure  161.  Such  a  structure  suggests 
at  once  various  kinds  of  musical  instruments  built  on  this 
plan.  The  soundingrboard  of  a  piano  is  fashioned  after 


Fig.  161.— DIAGRAM  SHOWING  THE  GRADUAL  LENGTHENING  OF  THE  CORDS  IN  THE  BASI- 
LAR MEMBRANE,  «,  d,  d,  d' ,  AND  THE  CORRESPONDING  INCREASE  IN  THE  WIDTH  OF 
THE  ORGANS  OF  CORTI,  a,  ft,  a,  6'. 

such  a  plan,  the  shorter  strings  of  the  board  representing 
the   treble   notes,  the  longer   ones    the   bass   notes.     This 


520 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


basilar  membrane  consists  of  about  3,000  such  strings  laid 
side  by  side.  Other  things  being  equal  the  lengths  of  these 
individual  strings  will  determine  the  pitch  of  their  vibra- 
tions, so  that  the  basilar  membrane  has  its  high  strings 
near  the  base  of  the  cochlea,  its  low  ones  near  the  top. 
This  basilar  membrane  is,  in  fact,  the  sounding-board  of 
the  ear,  and  the  various  strings  of  this  sounding-board  are 
set  up  in  sympathetic  vibrations  by  the  sound  waves  which 
pass  through  the  cochlea. 

It  will  be  remembered  that  the  sound  waves  from  the 
vestibule  ascend  the  cochlea  through  the  scala  vestibuli, 
and  while  ascending  this  they  do  not  affect  the  basilar  mem- 


Fig.  162.— SECTION  ACROSS  THE  BASAL  TURN  OF  THE  HUMAN  COCHLEA.  (After  Retzius.) 
D.  C,  scala  media;  s.  v,  scala  vestibuli;  s.  t,  scala  tytnpani;  R,  membrane  of  Reissner; 
Mt,  tectorial  membrane ;  6.  m,  basilar  membrane ;  t  C,  tunnel  formed  by  the  rods  of  Corti ; 
n,  nerve;  sp.  I,  spiral  lamina;  »•  sp,  sulcus  spiralis;  1.  sp,  spiral  ligament;  I,  limbus;  h,  i, 
inner  hair  cells;  h,  e,  outer  hair  cells,  with  hairs  from  same  projecting  through  the  reticu- 
lar  membrane. 

brane,  as  the  membrane  of  Reissner  intercepts.     At  the  top 
of  the  cochlea  the  sound  passes  into  the  scala  tympani,  and 


THE   EAR.  521 

while  descending  the  scala  tympani  the  vibrating  perilymph 
in  the  same  is  in  direct  contact  with  the  basilar  membrane 
and  at  this  point  sets  into  vibrations,  in  a  sympathetic  way 
already  explained,  the  strings  which  are  attuned  to  that 
particular  vibration.  In  other  words,  the  human  ear  is  but 
the  second  tuning-fork  set  into  motion  by  the  first  one.  It 
is  the  piano  that  responds  again  with  the  notes  sung  into  it. 
The  student  will  have  gone  far  in  understanding  the 
exact  manner  of  hearing  when  he  has  made  clear  to  himself 
the  complete  analogy  of  the  basilar  membrane  to  a  musical 
sounding-board  on  which  are  stretched  as  many  as  3,000 
differently  attuned  strings.  It  must  be  noticed  further  that 
the  proper  vibrations  of  these  strings  is  a  purely  physical 
result,  and  would  happen  in  a  dead  ear  or  an  ear  constructed 
out  of  metal  almost  as  readily  as  in  a  living  ear. 

2. — Rods  of  Corti.  Standing  on  this  basilar  membrane 
are  two  rows  of  rods  which  lean  towards  each  other  in  such 
a  way  as  to  form  a  tunnel  underneath.  These  two  series  of 
rods  are  called  the  rods  of  Corti.  One  series  rests  on  the 
basilar  membrane  just  at  the  point  where  it  is  attached  to 
the  lamina  spiralis;  the  other,  or  outer  rods,  rest  upon  the 
basilar  membrane  itself.  The  rods  next  to  the  lamina 
spiralis,  the  inner  rods,  seem  to  be  more  slender  and  are 
also  more  numerous  than  the  outer  rods,  the  numbers  be- 
ing about  6,000  and  4,500  respectively. 

At  the  base  of  the  cochlea  the  rods  of  Corti  are  higher 
but  stand  closer  together  than  they  do  towards  the  top, 
where  they  are  lower  and  wider.  (See  Figure  161.) 

3. — Reticular  Membrane.  Where  the  two  sets  of  rods 
meet  there  is  attached  a  membrane  which  extends  out 
horizontally  some  distance  over  the  basilar  membrane. 
This  membrane  is  called  the  reticular  membrane,  the  name 
being  derived  from  the  fact  that  it  is  pierced  with  very  many 
small  openings  through  which  the  hair  endings  of  the  audi- 
tory cells  beneath  extend. 


522  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

4. — Tectorium.  From  the  lamina  spiralis  there  extends 
a  membrane  over  the  rods  of  Corti  and  reticular  membrane 
called  the  tectorium  or  tectorial  membrane.  It  serves  for 
purposes  of  protection  to  these  delicate  structures  under- 
neath. The  groove  formed  between  the  lower  portions  of 
the  lamina  spiralis  and  the  tectorial  membrane  is  called  the 
sulcus  spiralis. 


D 

Fig.  163.— STRUCTURE  OF  A  SINGLE  ORGAN  OF  CORTI,  AND  TO  THE  RIGHT  THEIR  ARRANGE- 
MENT INTO  A  SERIES,  SUPPORTING  THE  FENESTRATED  RETICULAR  MEMBRANE. 

i,  internal  rod;  e,  external  rod;  t,  articulation  of  the  two  rods;  ft,  beginning  of  reticu- 
lar membrane;  n,  nerve;  6,  basilar  membrane. 

5. — Auditory  Hairs.  This  sulcus  spiralis  is  lined  with 
cuboidal  cells,  which  are  continued  over  the  margin  of  the 
basilar  membrane  as  columnar  cells,  some  of  which  bear 
on  their  upper  end  short,  stiff  hairs.  These  cells  between 
the  rods  of  Corti  and  the  sulcus  spiralis  are  termed  the 
inner  hair-cells.  Similar  cuboidal  cells  are  found  on  the 
basilar  membrane  beyond  the  rods  of  Corti,  which  cells  end 
in  delicate  stiff  hairs  that  project  through  the  openings  in 
the  reticular  membrane.  These  are  called  the  outer  hair- 
cells. 

Where  the  basilar  membrane  joins  the  outer  wall  of  the 
cochlea  these  cells  lose  their  cuboidal  appearance  and 
gradually  shade  off  into  the  ordinary  epithelium  which  lines 
the  outer  wall  and  the  inner  wall  of  the  membrane  of  Reiss- 
ner.  These  outer  and  inner  hair-cells  or  auditory  cells  are 
connected  at  their  bases  with  nerve  fibers  from  the  auditory 
nerve  reaching  them  through  the  lamina  spiralis.  The 
reader  to  orient  himself  properly  must  study  the  descrip- 
tion just  given  in  terms  of  the  accompanying  diagrams. 


THE   EAR.  523 

THE  FUNCTION  OF  THE  INDIVIDUAL  PARTS  OF  THE 
MEMBRANOUS  EAR. 

1. — Utriculus,  Saculus,  and  Semicircular  Canals. 
Regular  auditory  functions  were  formerly  attributed  to 
these.  The  suggestion  was  even  made  that  these  struc- 
tures aided  in  the  perception  of  noises,  while  to  the  cochlea 
was  referred  the  perception  of  musical  sounds.  Such  a 
distinction  is,  of  course,  absurd  at  once,  the  difference 
between  noise  and  music  being  a  physical  and  not  a  physi- 
ological one.  Later  Florens  and  Goltz  pointed  out  that 
these  structures  were  really  not  concerned  at  all  with  the 
direct  sense  of  hearing,  but  that  they  figured  as  organs  of 
equilibrium.  Animals  from  which  the  semicircular  canals 
have  been  removed  show  the  greatest  difficulty  in  standing 
still  or  moving  readily  and  with  precision.  They  seem  to 
be  unable  to  tell  the  position  of  their  bodies  and  show  all 
the  symptoms  ordinarily  associated  with  intense  dizziness. 
An  animal  so  robbed  of  these  structures  performs  the  most 
senseless  and  awkward  movements.  It  seems  perfectly  help- 
less and  is  scarcely  able  to  eat  unaided.  The  question  then 
arises,  in  what  manner  these  structures  figure  as  equilibrium 
organs. 

First.  The  three  semicircular  canals  are  arranged  like 
the  three  diameters  of  a  cube,  and  so  there  is  no  motion 
possible  which  does  not  fall  in  the  plane  of  one  or  more  of 
these  canals. 

Second.  These  canals  are  filled  with  endolymph  which 
is  in  communication  at  both  ends  with  the  utriculus  and  so 
is  able  to  circulate  somewhat  through  these  canals. 

Third.  A  movement  of  the  head  in  any  direction  will 
cause  a  backward  flow  of  the  endolymph  in  the  semicircular 
canal  affected,  due  to  the  inertia  of  that  liquid,  just  as  in 
the  starting  of  a  train  the  passengers  by  their  inertia  are 
thrown  backwards.  This  backward  motion  of  the  endo- 
lymph affects  the  hairs  projecting  into  it  in  the  ampulla 
somewhat  like  a  stream  of  air  over  a  field  of  grain,  and  in 


524  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

this  way  a  sensation  is  produced  which  in  the  mind  is  in- 
terpreted in  terms  of  position  or  movement.  If,  however, 
the  motion  in  a  certain  direction  should  continue,  the  endo- 
lymph  inside  would  soon  adjust  itself  to  that  motion,  just 
as  after  a  train  has  started  the  passengers  no  longer  feel  a 
tendency  to  be  thrown  backwards.  A  sudden  stopping  now 
of  the  train  throws  the  passengers  violently  forward.  So  a 
sudden  stopping  of  the  motion  of  the  body,  say  for  instance 
from  a  circular  motion,  will  cause  the  endolymph  on  ac- 
count of  its  inertia  to  be  thrown  forwards  and  in  this  way 
affect  the  projecting  hair  cells  and  give  rise  to  a  sensation 
of  motion.  Possibly  this  is  the  explanation  of  the  dizziness 
which  results  when  a  rotary  motion  of  the  body  suddenly 
ceases.  To  the  individual  it  seems  that  he  is  still  moving. 
One  point  in  favor  of  the  view  that  these  organs  are 
wholly  organs  of  equilibrium  is  the  fact  that  the  perception 
of  all  sounds  can  be  satisfactorily  explained  in  the  cochlea, 
and  so  there  is  no  necessity  to  begin  with  for  attributing 
auditory  sensations  to  these  structures.  On  the  other  hand, 
however,  none  of  the  invertebrates  have  a  cochlea,  and  yet 
it  would  be  entirely  wrong  to  think  that  these  animals  are 
without  the  sense  of  hearing.  Evidently,  therefore,  in  the 
invertebrates  at  least,  structures  very  analagous  indeed  to 
utriculus,  sacculus  and  ampulla  are  directly  concerned  in 
the  perception  of  sound,  and  it  may  be  possible  that  even 
in  the  human  being  this  property  has  not  been  entirely  lost, 
but  has  simply  been  overshadowed  by  the  addition  of  a  new 
structure  to  the  ear,  the  cochlea. 

2. — The  Function  of  the  Cochlea.  The  anatomy  of  the 
cochlea  readily  shows  how  a  vibration  descending  the  scala 
tympani  is  brought  in  direct  contact  with  the  basilar  mem- 
brane, and  how  there  by  sympathetic  vibrations  it  sets  into 
motion  some  one  of  the  many  strings  which  is  attuned  to  it. 
Arrangement  is  thus  made  in  purely  physical  ways  to  set  in 
vibration  the  proper  string  in  any  case,  but  it  is  an  equal 
physical  necessity  that  such  vibration  should  cease  as  soon 
as  the  sound  producing  it  ceases.  It  would,  of  course,  be 


THE    EAR.  525 

very  undesirable  to  have  the  basilar  string  in  the  ear  vibrate 
after  the  sound  producing  it  has  ceased.  Short,  sharp  stac- 
cato notes  would  be  an  impossibility  and  there  would  result 
in  the  ear  a  blending  and  running  together  of  sounds  which 
would  preclude  the  possibility  of  fine  music.  For  this  rea- 
son there  are  placed  dampers  on  these  strings,  much  after 
the  fashion  of  dampers  on  pianos.  The  rods  of  Corti  seem 
to  have  this  function.  Resting  continually  on  the  basilar 
membrane  they  so  weigh  down  these  strings  as  to  make 
them  cease  their  vibrations  as  soon  as  the  force  beneath 
them  producing  the  vibration  has  ceased.  Just  as  in  the 
case  of  a  piano  the  string  is  brought  to  quiet  when  the  pedal 
is  on,  as  soon  as  the  finger  is  taken  from  the  key. 

Up  to  this  point  everything  in  connection  with  the  ear 
has  been  purely  physical.  It  would  happen  in  a  dead  ear 
as  readily  as  in  a  living  one  provided  the  tissues  were  left 
intact,  but  there  now  remains  the  necessity  for  some  kind  of 
an  arrangement  by  means  of  which  the  vibrations  of  these 
strings  in  the  ear  may  be  communicated  to  the  brain.  This 
is  accomplished  by  means  of  the  auditory  cells  which  stand 
on  the  basilar  membrane  and  which  are  directly  connected 
with  the  auditory  nerve. 

When  a  certain  string  of  the  basilar  membrane  is  set  in 
motion  it  is  evident  that  the  hair  cells  resting  on  it  will  be 
moved  up  and  down  with  it,  and  possibly  this  vibratory  mo- 
tion of  the  hair  cells  serves  to  originate  a  nervous  impulse 
which  is  then  along  the  ordinary  channels  sent  to  the  brain 
and  there  interpreted  as  sound. 

A  second  possibility  exists.  The  long  stiff  hairs  which 
are  found  projecting  from  the  tops  of  these  auditory  cells 
pass  through  little  perforations  in  the  recticular  membrane, 
and  it  may  be  that  when  these  nervous  cells  move  up  and 
down  with  the  vibrations  of  the  cord  these  delicate  hairs  are 
rubbed  against  the  recticular  membrane  and  so  produce  a 
friction  which  serves  to  originate  a  nervous  impulse,  which 
then,  as  in  the  other  case,  finally  gives  rise  to  the  percep- 
tion of  sound.  That  it  must  be  either  the  movement  of  the 


526  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

cells  up  and  down  or  this  friction  of  their  delicate  hairs  in 
the  reticular  membrane,  or  possibly  both  of  these  which 
serve  as  a  stimulus  for  the  nervous  impulse,  is  beyond 
question. 

Here  is  the  point  at  which  the  physical  vibrations  give 
rise  to  physiological,  that  is,  nervous  impulses,  but  it  must 
be  borne  in  mind  after  all  that  the  real  conscious  apprecia- 
tion of  sound  occurs  only  in  the  auditory  centers  in  the 
brain.  Sound  is  a  purely  psychological  experience,  and  the 
ear  and  the  nerves  leading  from  it  to  the  brain  serve  merely 
as  accessory  pieces  of  apparatus  to  call  into  being  these 
psychical  acts. 

Very  few  sounds,  however,  are  so  simple  as  to  affect  but 
a  single  string  of  the  basilar  membrane.  Most  sounds  are 
composite  sounds  (hence  their  quality)  and  frequently 
composite  sounds  in  turn  are  blended  into  harmonies.  The 
ear,  however,  has  the  ability  to  perceive  all  the  individual 
sounds  that  enter  into  such  a  composition  and  so  we  must 
imagine  that  in  the  perception  of  the  concert  note  there  are 
as  many  strings  of  the  basilar  membrane  thrown  into  vibra- 
tion as  there  are  individual  component  notes  in  the  concert.- 
The  ear  is  even  able  to  analyze  such  a  concert  note  so  care- 
fully that  it  may  follow  some  of  the  individual  notes  in  it. 
No  one  finds  it  difficult  when  hearing  the  rendition  of  an 
orchestral  piece  of  music  to  follow  a  certain  instrument,  or 
in  a  chorus  to  listen  with  special  attention  to  a  certain 
voice.  This  analysis  is  possible  because  in  the  basilar 
membrane  as  many  individual  strings  are  affected  as  there 
are  such  component  notes. 

A  somewhat  interesting  question  arises  when  we  remem- 
ber that  although  the  ear  has  only  about  3,000  strings  it  is 
able  to  perceive  many  more  than  3,000  pitches.  This  may 
seem  at  first  inexplicable.  Possibly  the  explanation  may 
consist  in  assuming  that  when  a  pitch  is  sounded  which 
has  not  its  direct  counterpart  in  the  ear  but  lies  between 
the  pitches  of  two  adjoining  strings,  it  will  affect  both  of 
them,  and  this  possible  blending  may  give  rise  to  a  new 


THE    EAR.  527 

perception  of  pitch.  It  is  even  possible  to  imagine  that  the 
relative  strength  with  which  the  two  adjoining  strings  are 
affected  will  give  rise  to  a  corresponding  series  of  inter- 
mediate pitches. 

THE  LOCALIZATION  OF  SOUND. 

The  ability  which  we  possess  to  determine  the  direction 
from  which  a  sound  comes  is  an  acquired  ability.  In  local- 
izing a  sound  wre  instinctively  move  the  head  through  a 
series  of  positions  and  try  to  determine  in  which  position 
the  sound  is  clearest.  Having  once  found  this  position  we 
have  learned  by  experience  in  which  direction  we  must 
then  look.  When  the  head  is  held  perfectly  immovable  the 
localization  of  sound  is  very  difficult  indeed;  in  fact,  it  is 
almost  impossible  unless,  of  course,  the  sounds  be  so  near 
that  the  difference  in  the  acuteness  of  hearing  between  the 
two  ears  gives  us  a  clue  as  to  its  direction.  When  a  sound 
is  familiar  we  determine  its  distance  by  its  strength.  It  is, 
however,  a  purely  subjective  inference  which  it  is  possible 
to  vary  artificially,  as  for  instance  on  the  stage,  when  by 
soft  playing,  distance  is  suggested,  while  the  gradual 
strengthening  of  the  tones  is  interpreted  as  a  movement  of 
the  sources  of  music  towards  the  hearer. 

In  the  ear  there  are  sometimes  perceived  sounds  which 
are  not  produced  by  regular  sound  vibrations.  Such  sounds 
are,  for  instance,  the  buzzing  of  the  ears  produced  by  the 
vibrations  of  air  in  the  external  meatus,  when  this  air  has 
been  separated  from  the  external  atmosphere  by  bits  of  wax 
in  the  meatus,  or  by  vibrations  in  the  air  of  the  middle  ear, 
caused  by  an  unnatural  closing  of  the  Eustachian  tube. 
Beating  sensations  are  usually  caused  by  the  pulsations  of 
the  arteries  in  the  external  meatus.  Sensations  of  friction 
no  doubt  find  their  explanation  in  the  circulation  of  the 
blood,  while  the  peculiar  ringing  of  the  ears  which  some 
people  are  able  to  produce  at  will,  especially  when  they 
contract  the  muscles  of  mastication,  is  explained  by  some 
as  a  contraction  of  the  tensor  tyinpani,  and  so  a  stretching 


528  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

•r 

of  the  tympanic  membrane,  by  others  as  a  voluntary  open- 
ing of  the  Eustachian  tube. 

Finally,  it  is  of  interest  to  reflect  that  the  two  ears  are 
as  a  rule  attuned  alike,  at  least  so  nearly  alike  that  ordi- 
narily we  perceive  a  note  in  unison.  It  not  infrequently 
happens,  however,  that  there  is  such  a  difference  in  the  two 
ears  as  to  lead  to  the  perception  of  the  same  sound  at 
different  pitches,  a  pathological  condition  which  when  ag- 
gravated leads  to  the  most  serious  results  in  the  apprecia- 
tion of  tones.  No  less  remarkable  than  the  complete 
harmony  of  the  two  ears  is  the  continuance  of  such  har- 
mony through  all  the  vicissitudes  of  a  person's  life.  Few 
are  the  instruments,  indeed,  which  do  not  need  repeated  at- 
tention in  order  to  hold  them  at  their  proper  pitches.  In 
the  basilar  membrane  of  the  ear,  however,  this  attunement 
seems  not  only  one  of  remarkable  operation  to  begin  with, 
but  practically  never  requires  a  secondary  interference.  Its 
superiority  to  all  forms  of  artificial  musical  instruments  in 
the  number  of  notes  which  it  is  able  to  perceive,  in  the  ex- 
actness with  which  it  catches  and  reproduces  all  the  varied 
forms  of  the  sounds  which  reach  it,  and  in  the  accuracy 
with  which  it  remains  in  perfect  attunement,  may  well 
awaken  our  wonder  and  admiration. 


CHAPTER  XXIII. 


THE  EYE  AND  THE  PHYSIOLOGY  OF  VISION. 

That  the  eye  is  the  seat  of  vision  is  a  bit  of  knowledge 
as  old  possibly  as  humanity,  but  it  was  not  until  1602,  when 
Kepler  compared  the  human  eye  with  the  camera  obscura, 
that  any  considerable  attempt  was  made  in  the  explanation 
of  its  function.  Some  time  previous  Porta  had  invented  the 
camera  obscura,  and  so  it  was  but  a  natural  step  for  Kepler 
to  make  this  the  basis  for  his  explanation  of  the  eye.  Kep- 
ler's explanation  was  practically  nothing  more  than  merely 
the  statement  of  such  an  analogy  and  did  not  deal  with 
specific  details.  A  few  years  later,  1609,  the  Jesuit 
priest  Scheiner  noted  the  inversion  of  the  image  on  the  ret- 
ina, and  made  the  further  important  discovery  that  the 
pupil  contracted  or  expanded  with  the  varying  accommoda- 
tion of  the  eye.  In  1695  the  optician  Huyghens  constructed 
an  artificial  eye  and  demonstrated  on  the  same  the  action 
of  spectacles.  During  the  next  century  nothing  seemed  to 
be  added  to  the  knowledge  of  the  eye.  In  1801  Young 
(the  founder  of  the  present  Young-Helmholtz  Theory  of 
Vision)  noted  and  explained  astigmatism.  L,ong-sight  and 
short-sight  had  been  previously  observed,  and  Huyghens 
had  actually  explained  the  action  of  spectacles  in  remedy- 
ing these  defects. 

Up  to  the  beginning  of  this  century,  and  even  later, 
nothing  was  known  of  the  manner  in  which  the  eye  was 
accommodated  for  far  and  near.  The  necessity  for  such  a 
power  of  accommodation  had  been  noted  by  Kepler,  and 
Descartes  had  actually  suggested  the  thought  that  the 
power  of  accommodation  resulted  from  the  ability  of  the 
lens  to  change  its  form,  but  it  was  not  until  1801  that 
Young  demonstrated  this  change  in  experiments  on  his  own 
34  (529) 


530  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

eyes.  Objectively  this  change  in  the  form  of  the  lens  was 
demonstrated  by  the  reflection  of  images  from  the  surfaces 
of  the  lens,  by  L,angenbeck  in  1849,  and  verified  by  Helm- 
holtz  in  1853.  The  ciliary  muscles  had  been  noted  by 
Briicke  in  1846,  and  in  1856  Helmholtz  attributed  the 
motor  agency  in  accommodation  to  this  muscle,  and  for- 
warded the  theory  of  accommodation  as  it  still  stands.  The 
innervation  of  this  muscle  was  discovered  by  Hensen  and 
Volckers  in  1868.  The  finer  structure  of  the  retina  was 
worked  out  by  H.  Muller's  researches  on  the  eye,  1855, 
although  as  early  as  1851  Helmholtz  had  designated  the 
rods  and  cones  as  the  points  sensitive  to  light.  The  blind 
spot  had  been  discovered  by  Mariotte  as  early  as  1668.  In 
1876  the  vision  purple  found  in  the  rods  was  discovered  by 
Boll. 

Our  knowledge  of  the  physiology  of  color  sensations  has 
been  of  slow  growth.  In  1657  the  celebrated  Newton  in  his 
studies  on  the  spectrum  discovered  the  different  refractive 
indices  of  the  different  colors  and  their  composition  into 
white  light.  In  1690  Huyghens  proposed  the  wave  theory  of 
light,  while  in  1746  Euler  demonstrated  that  the  difference 
in  colors  depends  on  the  rate  of  light  vibrations,  or  what  is 
the  same  thing,  the  length  of  the  waves.  A  theory  of  color 
sensations  was  advanced  by  Young  in  1807  which  modified 
by  Helmholtz  is  to-day  possibly  still  the  best  explanation  at 
hand.  The  Young-Helmholtz  theory  does  not,  however, 
offer  a  satisfactory  explanation  for  several  observed  facts, 
and  to  include  these  a  second  entirely  different  theory  was 
advanced  by  Ewald  Hering  in  1872.  Quite  a  number  of 
other  observers  have  added  to  our  knowledge  on  this  sub- 
ject. Such  has  been  in  briefest  outline  the  path  of  the  dis- 
coveries which  have  led  to  our  present  understanding  of  the 
eye.  It  may  be  in  place  at  this  point  to  add  that  there  re- 
mains very  much  still  unexplained  about  the  eye,  and  that 
there  are  few  subjects  in  physiology  concerning  which  ad- 
ditional information  is  more  sorely  wanted. 


THK   EYE   AND   THE   PHYSIOLOGY   OK   VISION.  531 

SOME  OF  THE  ELEMENTARY  PHYSICAL  CONCEPTIONS   OF  LIGHT 

NECESSARY  TO  A  PROPER  UNDERSTANDING  OF  THE 

PHYSIOLOGY  OF  THE  EYE. 

The  eye  is  a  complicated  piece  of  apparatus  especially 
designed  to  translate  light  impressions  into  nervous  impres- 
sions. Its  construction  is  for  a  specific  purpose  and  its 
anatomy  dependent  upon  the  physical  properties  of  the 
light  it  is  to  translate.  It  is,  therefore,  entirely  impossible 
to  understand  the  raison  d^etre  of  the  eye's  structure  with- 
out having  an  elementary  conception  at  least  of  some  of  the 
physical  properties  of  light. 

1. — The  Nature  of  Light.  For  a  long  time  light  was 
looked  upon  as  small  particles  of  matter  projected  in  straight 
lines  from  a  luminous  body.  These  little  particles  passed 
into  the  eye,  and  there  in  some  way  produced  the  sensation 
of  light.  A  lamp,  therefore,  would  be  something  like  a 
spherical  Gatling-gun  throwing  its  missiles  in  every  con- 
ceivable direction  at  a  very  great  velocity.  These  particles 
were  looked  upon  as  exceedingly  small  and  light,  and  able 
to  penetrate  even  such  hard  substances  as  glass. 

This  material  projection  of  light  had  soon  to  be  aban- 
doned as  thoroughly  unable  to  explain  all  of  the  phenomena 
at  hand.  As  a  result  of  more  exacting  study  there  was  ad- 
vanced soon  what  is  now  familiarly  known  as  the  undulatory 
theory  of  light,  the  theory  which  conceives  of  light  as  oscil- 
lations or  waves  of  some  suitable  medium.  This  medium 
is  the  ether,  possibly  a  hypothetical  substance,  and  yet  one 
to  the  actual  existence  of  which  we  are  driven  by  the  ne- 
cessity of  the  mind. 

This  ether  is  a  very  light  imponderable  medium  offering 
little  if  any  resistance  to  objects  moving  through  it.  It  not 
only  pervades  all  space,  but  seems  also  to  pervade  many 
solid  objects,  such  as  glass  and  others  which  we  are  wont 
to  call  transparent.  Rays  of  light  are  conceived  as  vibra- 
tions passing  through  this  medium,  in  which  the  actual 
particles  of  the  medium  move  but  little  out  of  their  place, 


532  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

while  the  wave,  however,  transmitted  from  particle  to  par- 
ticle travels  with  inconceivable  rapidity.  Speaking  gen- 
erally, light  is  like  sound  —  a  wave  motion,  but  these  waves 
differ  in  several  respects  from  each  other.  In  the  case  of 
light  the  medium  is  ether  and  in  sound  air,  or  water,  or 
solids.  The  rapidity  of  transmission  is  very  different,  and 
the  form  of  the  wave  is  quite  unlike  that  of  the  sound  wave. 
In  the  transmission  of  a  sound  wave  through  the  air  the 
particles  of  air  carrying  the  wave  move  backwards  and  for- 
wards in  the  direction  in  which  the  sound  is  moving.  In 
light,  however,  the  individual  particles  of  ether  move  at 
right  angles  to  the  direction  of  the  ray  of  light.  If  it  were 
possible  to  picture  a  ray  of  light  approaching  one  it  would, 
using  a  very  rough  analogy  indeed,  look  somewhat  like  a 
wheel,  the  hub  being  the  line  of  direction,  while  the  indi- 
vidual spokes  would  represent  the  directions  in  which  the 
particles  of  ether  are  thrown  by  the  wave  at  that  point.  If 
one  could  now  think  of  such  a  wheel  squarely  approaching 
one  and  imagine  the  spokes  radiating  from  it  in  every  di- 
rection to  be  rapidly  drawn  into  the  hub  and  projected 
again,  one  would  have  a  very  rough  idea  of  the  picture  of 
an  approaching  wave  of  light. 

2. — The  Rate  of  Transmission.  It  was  impossible  for  a 
long  time  to  make  actual  calculations  of  the  rate  with  which 
a  ray  of  light  travels,  as  its  rapidity  was  so  great  that  for  all 
practical  purposes  it  was  instantaneous.  The  opportunity 
of  measuring  light  passing  through  immense  distances  pre- 
sented itself  when  the  phases  of  the  satellites  of  Jupiter  were 
carefully  noted.  When  the  earth  is  between  the  sun  and 
Jupiter,  that  is  as  close  to  Jupiter  as  its  orbit  permits,  the 
time  for  the  phases  of  one  of  Jupiter's  satellites  was  carefully 
determined.  Six  months  later  the  earth  is,  of  course,  further 
removed  from  Jupiter  by  the  distance  of  the  earth's  orbit. 
Calculations  now  showed  that  the  phases  of  the  satellite  in 
question  were  a  little  over  sixteen  minutes  slow.  The  ex- 
planation of  the  sixteen  minutes'  tardiness  consisted  in  at- 
tributing this  loss  of  time  to  the  time  required  by  the  light 


THE   EYE   AND  THE   PHYSIOLOGY   OF  VISION.  533 

to  pass  the  added  distance  of  the  earth's  orbit.  In  other 
words,  it  took  a  ray  of  light  a  little  over  sixteen  minutes  to 
cross  the  earth's  orbit,  a  distance  of  some  one  hundred  and 
eighty  million  miles.  This  makes  the  distance  traveled  per 
second  about  186,000  miles. 

Thus,  a  ray  of  light  would  have  a  sufficient  speed  to  travel 
around  the  earth's  surface  about  seven  or  eight  times  be- 
tween two  successive  ticks  of  a  second  hand. 

3. — The  Number  of  Vibrations  in  Waves  of  Light.  If 
light  is  a  wave  motion  the  problem  presents  itself  of  having 
the  number  of  vibrations  per  second  measured.  Without 
going  into  the  physical  explanation  of  the  manner  in  which 
this  is  accomplished,  save  the  statement  that  such  measure- 
ments have  been  made  and  the  number  of  vibrations  per 
second  determined  with  relative  accuracy,  the  interesting 
fact  at  once  comes  to  light  that  the  number  of  vibrations 
determines  the  color  of  the  light  just  as  in  the  case  of 
sound  the  number  of  vibrations  determines  the  pitch.  The 
pitch  of  a  light  is  its  color.  The  lowest  pitch  in  light 
visible  to  the  eye  is  red;  the  highest  pitch  is  violet.  When 
the  vibrations  become  less  frequent  than  those  in  red  or 
more  numerous  than  those  in  violet  they  do  not  affect  the 
eye  and  seem  like  perfect  darkness.  This  darkness  below 
the  red  and  above  the  violet  is,  however,  not  a  physical 
darkness;  it  is  a  physiological  darkness.  Even  though  the 
etherial  vibrations  are  there  the  physiological  capacity  of 
the  eye  is  not  large  enough  to  include  them. 

Using  approximate  figures  only,  there  are  in  red  light 
400,000,000,000,000  per  second;  in  violet,  800,000,000,- 
000,000.  The  lowest  base  note  in  light  consists  of  four 
hundred  trillions ;  the  highest  note  of  eight  hundred  trillions 
per  second.  Between  these  two  extreme  pitches  of  color 
are  the  other  colors  of  the  spectrum.  Thus  green,  which 
is  about  half  way  between  the  red  and  violet,  has  in  the 
neighborhood  of  six  hundred  trillions. 

4. — The  Spectrum.  Ordinary  sunlight,  the  ordinary 
light  of  the  day,  is  what  we  usually  designate  " white" 


534  STUDIES    IN    ADVANCED   PHYSIOLOGY. 

light.  This  white  light  is  not  a  simple  light  but  consists 
of  all  the  vibrations  from  the  red  to  the  violet.  In  other 
words,  white  light  is  a  concert  of  all  the  pitches  of  light. 
In  music  we  are  able  to  analyze  the  individual  sounds  that 
go  into  a  complicated  harmony,  but  in  light  the  eye  is  un- 
able to  make  such  an  analysis,  and  this  combination  of  all 
of  the  colors  of  the  spectrum  is  perceived  as  one  color  and 
called  white. 

By  means  of  a  prism  it  is  possible  to  separate  this  white 
light,  to  analyze  it,  and  get  each  color  by  itself.  The  re- 
sult of  such  a  procedure  is  the  spectrum  familiar  to  every 
one,  if  not  in  the  laboratory,  at  least  in  the  rainbow.  By 
means  of  such  a  prism  the  colors  are  strung  out,  from  the 
red  at  one  end  to  the  violet  at  the  other,  and  the  position  of 
each  color  is  determined  by  the  number  of  vibrations  per 
second  which  it  has.  Commonly  we  say  that  in  this  scale 
we  are  able  to  perceive  seven  distinct  colors.  These  are: 
red,  orange,  yellow,  green,  blue,  indigo,  violet. 

Reference  to  the  number  of  vibrations  in  red  light  and 
violet  light  shows  that  violet  light  is  just  an  octave  above 
red  light.  It  possesses  just  about  twice  the  number  of 
vibrations,  and  it  is  extremely  interesting  to  note  that  at 
the  violet  end  the  red  reappears.  In  fact,  violet  is  nothing 
but  the  blue,  with  which  is  mixed  a  little  red,  possibly  the 
red  of  the  next  octave.  It  is  apparent,  therefore,  that  our 
range  of  vision  extends  over  but  one  octave  of  colors,  from 
the  red  at  the  lower  end  to  the  red  at  the  upper  end,  where 
it  reappears  to  blend  with  the  blue  forming  the  violet. 
What  the  color  sensations  would  be  if  the  range  of  vision 
should  extend  over  more  than  one  octave  it  is  entirely  im- 
possible to  say.  If,  however,  they  should  be  reproductions 
of  the  first  octave  one  can  see  that  nothing  would  be  gained 
by  their  presence  as  far  as  new  colors  are  concerned,  and 
as  the  eye  is  perfectly  unable  to  analyze  a  compound  color, 
is  unable  to  perceive  its  inherent  harmony,  there  is  but 
an  added  reason  for  the  limitation  of  the  range  of  vision  to 
a  single  octave. 


THE   EYE   AND   THE   PHYSIOLOGY  OF  VISION.  535 

The  seven  colors  of  the  spectrum  are  usually  spoken  of 
as  the  fundamental  colors,  because  by  the  mixture  of  two 
or  more  of  these  it  is  possible  to  produce  all  the  other 
colors.  Thus  the  proper  combination  of  all  seven  forms 
white;  the  absence  of  all  of  them  gives  the  perception 
black.  Black  is  in  light  what  a  rest  is  in  music,  but  while 
in  the  ear  a  rest  is  perceived  as  the  absence  of  any  positive 
sensation,  in  the  eye  an  absence  of  all  light  is  interpreted 
as  a  positive  sensation,  and  so  black  seems  to  be  a  definite 
color.  By  mixing  any  of  the  fundamental  colors  with  white 
we  get  the  varying  tints  of  these  colors ;  by  mixing  them 
with  black  the  corresponding  shades.  Thus  red  and  white 
make  pink,  red  and  black  brown;  green  and  white  produce 
light  green,  green  and  black  olive,  blue  and  white  the  light 
blues,  blue  and  black  the  blue  blacks.  Red  and  blue  form 
purple,  purple  and  green  produce  white.  Mixing  colors 
near  each  other  in  the  spectrum  produces  an  intervening 
color.  Thus  red  and  yellow  form  orange. 

It  must  be  especially  borne  in  mind  that  in  all  instances 
of  the  combinations  just  given  the  sensations  are  mixed  and 
not  pigments.  Thus  on  a  color  disk  partly  red  and  partly 
blue  the  color  purple  will  arise  upon  a  rapid  rotation  of 
that  disk.  If  one  should  mix  pigments  quite  a  different  re- 
sult would  occur.  To  mix  red  and  blue  combined  in  cer- 
tain proportions  produces  not  purple  at  all,  as  when 
sensations  are  mixed,  but  produces  green,  the  explanation 
of  which  will  be  given  further  on. 

5. — Complementary  Colors.  Two  colors  (sensations) 
which  when  mixed  together  produce  white,  are  spoken 
of  as  complementary  colors.  For  each  color  of  the  spec- 
trum it  is  possible,  if  the  color  purple  be  added,  to  find  a 
second  color  complementary  to  it.  The  relations  of  these 
colors  are  given  in  Figure  164,  where  the  colors  of  the 
spectrum  are  so  arranged  that  those  directly  opposite  each 
other  from  the  point  called  white  are  complementary.  The 
use  of  indigo  or  blueing  in  the  process  of  laundering  con- 


536  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

sists  in  neutralizing  the    yellow  of   the  linen,   yellow  and 
indigo  forming  white. 


Blue 


Fig.  164.— GRAPHIC  REPRESENTATION  OF  THE  FORMATION  OF  WHITE  OUT  OF  THE  SERIES 

OF  COMPLEMENTARY  COLORS. 

The  line  frohi  the  green  should  be  continued  to  the  purple,  as  green  and  purple  are 
complementary  colors. 

6. — The  Colors  of  Objects  by  Transmitted  or  Reflected 
Light.  So  far  the  colors  have  been  described  as  vibrations 
of  ether  proceeding  from  a  luminous  body,  and  by  the 
number  of  such  vibrations  per  second  the  light  will  have 
its  color  determined.  But  most  bodies  are  not  luminous;  a 
window  pane  is  not  luminous  but  transmits  light  through 
it ;  the  wall  of  a  house  is  not  luminous  but  is  seen  only  by 
the  light  which  it  reflects  from  some  luminous  source. 
Ordinarily  this  transmitted  or  reflected  light  is  sunlight. 
Even  though  the  rays  of  the  sun  do  not  shine  directly  into 
the  room,  some  of  the  rays  have  been  reflected  by  the  grass 
or  sky,  or  objects  on  the  ground  in  such  a  way  as  to  reach 
the  wall  in  question,  and  being  reflected  from  this  in  turn 
into  the  eye,  the  wall  becomes  visible. 

The  question  then  presents  itself,  what  determines  the 
color  of  such  a  transparent  piece  of  glass  or  of  the  opaque 
wall? 

First,  objects  colored  by  transmitted  light.  A  red  win- 
dow pane  seems  red  because  it  has  absorbed  all  the  other 
colors  in  the  light  which  passes  through  it,  but  transmits 
unhindered  the  red  light  reaching  it.  Like  the  gold  digger 


THE    EYE    AND    THE    PHYSIOLOGY   OF   VISION.  537 

who  picks  out  of  the  sands  the  yellow  gold,  but  allows 
the  white  sands  to  be  washed  through  his  fingers,  so  this 
window  pane  picks  out  all  the  colors  of  the  spectrum,  while 
the  red  color,  like  the  sand  in  the  analogy,  it  allows  to  pass 
through.  We  can  easily  understand  how  a  boy  looking 
over  an  assortment  of  marbles  would  pick  out  for  his  own 
use  and  put  into  his  pocket  all  those  of  certain  desirable 
colors  and  reject  possibly  all  those  of  some,  to  him,  unsatis- 
factory color.  So  this  window  pane  picks  out  and  absorbs 
from  the  composition  of  colors  which  reach  it  in  the  white 
light  certain  colors,  while  it  rejects,  that  is,  allows  to  pass 
without  hindrance,  the  red  light  which  falling  into  the  eye 
finally  arouses  there  the  corresponding  sensation.  It  is  evi. 
dent  that  such  a  window  pane  could  look  red  only  when  red 
light  reached  it,  since  that  is  the  only  light  it  allows  to  pass 
through.  If  blue  light  alone  should  reach  it  the  blue  would 
be  entirely  absorbed  and  the  result  would  be  no  light  at  all 
traversing  it,  the  window  pane  would  look  black.  One  may 
easily  try  the  experiment  of  looking  through  a  piece  of  red 
glass  at  an  intensely  blue  object.  The  red  glass  is  opaque 
to  the  blue.  A  similar  experiment  would  be  to  take  a  red 
glass  and  a  blue  glass  and  let  a  beam  of  light  pass  through 
both.  As  this  beam  of  wfcite  light  passes  through  the  blue 
glass  plate  all  the  red  and  yellow  would  be  absorbed  and 
nothing  but  the  blue  be  permitted  to  pass.  But  blue  light 
is  absorbed  by  the  red  pane,  which  allows  only  red  light  to 
pass  through,  but  as  all  the  red  light  was  absorbed  by  the 
blue  plate,  no  light  at  all  passes  through.  The  two  trans- 
parent glasses  act  like  an  opaque  object. 

Second,  what  is  the  explanation  of  the  color  of  the  objects 
around  us,  such  as  the  cover  of  a  book,  the  tint  of  a  ribbon, 
or  the  shade  of  a  paint  ?  The  explanation  is  similar  to  that 
given  in  the  case  of  transmitted  light.  White  light  falls  on 
the  ribbon,  and  if  this  ribbon  should  reflect  all  the  light 
that  it  received,  it  too,  would  appear  white.  But  the  rib- 
bon absorbs  some  of  the  colors  and  reflects  only  those  colors 
which  it  cannot  absorb.  In  the  case  of  the  red  ribbon, 


538  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

green,  blue,  violet,  and  even  some  yellow  are  absorbed,  and 
so  only  the  red  light  remains  to  be  reflected.  A  rather  far- 
fetched analogy  might  be  found  in  throwing  against  a  wall 
a  handful  of  different  objects,  nearly  all  of  them  very  sticky 
indeed,  but  mixed  with  these  several  elastic  rubber  balls. 
If  such  a  handful  of  objects  were  hurled  against  a  wall,  not 
all  of  them  would  be  reflected.  Most  of  the  sticky  objects 
would  remain  attached  to  the  wall,  and  possibly  the  rubber 
balls  alone  be  reflected.  So  in  the  sunlight,  which  is  a 
mixture  of  the  fundamental  colors,  practically  all  of  the 
colors  are  absorbed  by  the  ribbon,  while  the  red,  like  the 
rubber  ball  in  the  analogy,  is  reflected,  and  as  we  judge  of 
the  color  of  an  object  by  the  light  which  comes  from  it,  we 
designate  it  as  red.  As  a  matter  of  fact,  however,  the  color 
of  an  object  by  reflected  light  is  always  the  color  which  it 
has  rejected. 

7. — The  Refraction  of  Light  and  the  Property  of  Lenses. 
Light  passes  in  straight  lines  through  a  medium  of  uniform 
density.  If,  however,  it  passes  from  a  less  dense  to  a  more 
dense  medium  it  is  bent  from  its  course.  Such  a  bending 
of  rays  of  light  is  called  refraction,  and  upon  this  property 
of  light  depends  the  use  of  lenses.  A  lens  is  nothing  more 
than  a  transparent  medium  of  greater  density  than  the  air, 
and  so  will  bend  the  rays  of  light  from  their  original  direc- 
tion. It  would  be  entirely  out  of  place  in  this  discussion  to 
go  into  detail  in  the  matter  of  refraction,  and  it  will  suffice 
to  call  attention  to  the  ordinary  kinds  of  lenses  and  the 
manner  in  which  they  refract  the  light. 

Convex  lenses,  either  convex  on  both  sides  (double  con- 
vex lens)  or  plain  on  one  side  (single  convex  lens)  bend 
the  rays  of  light  together,  and  if  the  lens  be  a  fairly  good 
one,  all  the  rays  in  a  beam  of  light  may  be  finally  bent  so 
as  to  meet  at  a  certain  point  back  of  the  lens  known  as  the 
focus.  The  amount  of  the  bending  of  the  rays  will  depend, 
other  things  being  equal,  upon  the  convexity  of  the  lens, 
being  greater,  the  greater  the  convexity.  Illustrations  of 
such  results  are  familiar  to  ever  one  in  the  ordinary  burning 


THE    EYE    AND    THE    PHYSIOLOGY   OF   VISION. 


539 


glasses,  by  means  of  which  the  parallel  rays  of  the  sun  are 
concentrated  at  one  point  sufficiently  to  start  ignition. 

If  the  lens  be  concave,  either  on  both  sides  (double  con- 
cave) or  on  one  side  (single  concave)  the  rays  of  light  will 
be  bent  apart;  that  is,  scattered.  This  action  of  lenses  will 
be  more  evident  by  comparison  of  Figures  165  and  166, 
where  the  course  of  rays  of  light  through  such  lenses  is 
shown  by  a  series  of  lines.  Some  lenses  may  be  concave  on 
one  side  and  convex  on  the  other,  called  concavo-convex 
lenses,  and  such  lenses  will  either  converge  the  light  or 
scatter  the  light,  according  as  the  convexity  is  greater  or  less 
than  the  concavity. 


Fig.  165.— To  SHOW  THE  CONVERGING  ACTION  OF  A  CONVEX  LENS. 


Fig.   166.— TO  SHOW  THE  DISPERSIVE  ACTION  OF  A  CONCAVE  LENS. 

F,  the  focus  at  which  the  dispersed  rays  would  meet  if  continued. 

For  the  purpose  of  understanding  the  eye  it  is  especially 
desirable  to  bear  in  mind  the  fact  that  the  convexity  of  a 
lens  will  determine  the  extent  of  the  refraction  of  the  light 
through  it  and  also  the  position  of  a  focus  back  of  it.  The 
more  convex  the  lens  is  the  closer  will  be  the  focus  behind 
the  lens,  the  less  convex  it  is  the  further  removed  from  the 
lens  will  be  this  focus.  Upon  these  simple  considerations 


540  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

of  the  refraction  of  light  is  based  the  use  of  spectacles,  and 
even  the  use  of  the  eye  itself,  this  containing  within  itself 
several  refracting  media  which  obey  in  every  way  the  physi- 
cal laws  that  govern  light  refraction. 

8. — The  Formation  of  Images  by  Lenses.  By  means  of 
a  good  lens  or  a  system  of  lenses  there  may  be  produced 
an  image  of  an  object  placed  in  front  of  the  lens.  The 
microscope,  the  telescope  and  the  photograph  camera  at- 
test this  fact.  In  the  camera  a  sensitive  plate  is  put  back 
of  the  lens  in  such  a  position  that  the  image  produced  by 
the  lens  falls  directly  on  it,  and  there  in  chemical  ways 
leaves  its  impress  on  the  sensitive  plate.  There  is  in  the 
eye  an  exactly  analogous  result,  the  eye  being  in  practically 
every  particular  a  high  grade  camera  in  which  the  sensitive 
plate  is  replaced  by  the  still  more  sensitive  retina,  and  in 
order  to  perceive  objects  clearly  the  image  produced  by  the 
lens  and  humors  of  the  eye  must  fall  directly  upon  the  re- 
tina. The  point  under  explanation  here  is  to  show  under 
what  circumstances  an  image  arises.  An  image  results 
when  a  number  of  rays  of  light  emanating  from  the  same 
point  are  so  bent  by  a  lens  as  to  meet  again  at  a  certain 
point  back  of  the  lens.  As  the  rays  of  light  from  any  point 
on  a  luminous  body  radiate  in  every  direction;  that  is, 
diverge  more  and  more,  it  is  evident  that  they  would  never 
meet  unless  these  divergent  rays  should  be  bent  together 
by  some  refracting  medium;  hence  no  image  is  possible 
when  the  lens  is  removed.  The  function  of  the  lens  is  to 
collect  this  divergent  pencil  of  rays  from  the  point  in  qiies- 
tion,  and  bend  it  together  to  meet  in  a  corresponding  point 
back  of  the  lens. 

If  at  this  second  point  a  screen  be  held  there  appears  an 
image  the  exact  counterpart  of  the  object.  But  any  object 
consists  of  but  an  infinite  number  of  individual  points,  and 
so  it  is  the  function  of  the  lens  to  take  the  divergent  rays 
from  each  of  these  infinite  points  and  converge  them  to  a 
corresponding  number  of  infinite  points  behind  the  lens. 


THE    EYE    AND    THE    PHYSIOLOGY   OF   VISION.  541 

In  this  manner  there  arises  the  complete  image  of  the  entire 
object.  Figure  167  shows  this  action  of  the  lens  for  two 
•given  points.  Reference  to  it  will  also  show  that  the  image 
will  be  inverted.  This  is  also  true  of  the  image  on  the  retina. 
With  these  physical  conceptions  of  the  nature  of  light 
and  its  properties  we  are  ready  to  understand  with  more 
meaning  the  detailed  anatomy  of  the  eye. 


Fig.  167.— DIAGRAM  TO  ILLUSTRATE  THE  REFLECTION  AND  THE  REFRACTION  OF  LIGHT. 
At  A  the  beam  of  light  is  reflected,  illuminating  the  arrow  a  c,  at  B.  From  all  points 
of  the  arrow  a  c,  the  light  is  reflected  in  all  directions.  Two  such  divergent  beams  are 
shown  as  refracted  by  the  convex  lens  L  L,  and  brought  to  points  a'  and  c',  producing  at 
these  points  images  of  the  points  a,  c.  As  this  is  true  for  all  points  on  a  c,  there  will  be  a 
complete  image  at  a'  c'.  The  lines  at  S'  S',  and  S"  S",  show  positions  of  screen  where 
the  image  is  blurred. 

THE  ANATOMY  OF  THE  EYE. 

While  the  eyeball  itself  contains  the  sensitive  retina  and 
the  refracting  media,  and  so  the  essential  parts  of  the  eye, 
it  is  provided  with  a  number  of  appendages  which  make  its 
use  in  vision  much  more  efficient.  On  account  of  its  sen- 
sitiveness it  needs  special  organs  for  protection.  A  system 
of  muscles  enable  it  to  make  rapid  movements,  while  a 
lachrymal  apparatus  protects  it  from  an  accumulation  of 
dust  and  other  foreign  particles. 

1. — The  Eyebrows.  The  function  of  these  is  so  ap- 
parent from  every-day  experience,  preventing  the  perspira- 
tion of  the  forehead  from  running  over  the  eyeball  but 
turning  it  aside  down  the  cheeks,  that  further  statement  is 
unnecessary.  That  they  act  in  shading  the  eye  is  probably 
only  exceptionally  true. 


542  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

2. — The  Eyelids.  Each  eye  is  provided  with  two  main 
eyelids  and  the  remnant  of  a  third.  Of  these  the  upper 
eyelid  is  the  one  which  has  the  greatest  range  of  motion, 
and  by  the  movements  of  which  the  lachrymal  secretion  is 
being  continually  washed  across  the  globe.  In  addition  to 
distributing  the  tears  it  serves  purposes  of  protection  against 
foreign  particles  and  for  the  exclusion  of  light  when  that 
is  too  intense,  or  when,  as  in  sleep,  it  is  to  be  excluded 
altogether.  The  functions  of  the  upper  eyelid  apply  to  a 
certain  extent  equally  to  the  lower  eyelid. 

At  the  edge  of  these  eyelids  are  found  the  eyelashes, 
rows  of  hairs  serving  to  prevent  foreign  particles  from  get- 
ting into  the  eye,  and  possibly  shading  the  cornea.  Be- 
tween these  hairs  open  the  ducts  of  specially  developed 
sebaceous  glands,  known  as  the  Meibomian  glands,  which 
secrete  a  fatty  substance  specially  evident  in  certain  cases 
of  inflammation,  where  this  secretion  becomes  so  excessive 
as  to  stick  the  eyelids  together.  This  secretion  serves  not 
only  to  keep  the  edge  of  the  eyelids  pliable,  but  prevents  the 
tears  from  running  over  the  eyelids,  it  being  a  general  phy- 
sical fact  that  water  does  not  readily  flow  over  an  oily 
surface.  Of  course  in  the  act  of  crying  the  amount  of  the 
secretion  increases  so  much  that  this  oily  edge  no  longer 
serves  as  a  sufficient  barrier,  and  so  the  tears  stream  down 
the  cheeks. 

Lining  the  under  sides  of  the  eyelids  both  upper  and 
lower  and  reflected  back  over  the  front  of  the  cornea  is  the 
conjunctiva.  Few  membranes  in  the  body,  especially  those 
exposed  to  the  exterior,  are  so  richly  supplied  with  nerves 
and  so  sensitive  to  all  foreign  objects.  The  explanation  of 
placing  such  a  very  sensitive  membrane  under  the  eyelids 
and  over  the  cornea  lies  in  the  fact  that  it  prevents  us  from 
becoming  careless  about  injurious  particles  reaching  the 
eye,  and  so  gives  iis  no  rest  until  the  irritating  object  is 
removed. 

The  lifting  of  the  upper  eyelid  is  effected  by  muscles 
running  down  into  the  eyelid.  The  closing  of  the  eye  is 


THE   EYE   AND    THE    PHYSIOLOGY   OF   VISION.  543 

due  to  the  contraction  of  a  circular  muscle  which  runs 
through  the  upper  and  lower  eyelids  and  so  encircles  the 
open  space  which  separates  the  upper  from  the  lower  lid. 

In  addition  to  the  two  regular  eyelids  there  is  present  in 
man  the  rudiment  of  a  third  eyelid.  This  may  be  readily 
observed  as  a  red  vertical  fold  at  the  inner  corner  of  the 
eye,  and  in  some  individuals  reaching  almost  to  the  iris. 
This  eyelid  is  especially  developed  in  many  animals,  such 
as  birds,  and  can  by  these  animals  be  drawn  entirely  over 
the  front  of  the  eyeball.  When  so  fully  developed  it  is 
called  the  nictitating  membrane. 

In  this  remnant  of  the  nictitating  membrane  is  a  small 
reddish  elevation  readily  recognizable  called  the  caruncula 
lachrymalis,  consisting  of  a  number  of  sebaceous  glands 
imbedded  in  this  fold. 

3. — The  Lachrymal  Apparatus.  To  keep  the  surface 
of  the  eyeball  perfectly  clear  and  to  remove  particles  of 
dust,  there  is  provided  for  each  eye  a  lachrymal  apparatus 
consisting  of  a  tear  gland  and  a  system  of  ducts. 


Fig.  168.— THE  LACHRYMAL  APPARATUS. 

1,  lachrymal  gland;  2,  lachrymal  ducts;  3,  3,  the  puncta  lachrymalia ;  4,  the  nasal  sac; 
5,  the  nasal  duct. 

The  lachrymal  or  tear  gland  lies  not  in  the  inner,  but  in 
the  upper  and  outer  part  of  the  orbit  under  the  edge  of  the 
frontal  bone.  It  is  about  the  size  of  an  almond.  From 
this  gland  (which  histologically  is  an  ordinary  racemose 


544  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

gland) ,  run  quite  a  number  of  ducts  which  open  in  a  row 
under  the  upper  eyelid.  From  this  point  the  secretion  is 
washed  over  the  front  of  the  eye  by  the  ordinary  movements 
of  the  eyelids,  such  as  those  of  winking,  and  so  the  cornea 
is  kept  moist  and  clear  and  free  from  dust.  The  secretion 
is  finally  led  off  by  two  lachrymal  canals,  which  arise  each  as 
a  small  pore  called  the  punctum  lachrymalis  found  on  each 
lachrymal  papilla.  These  lachrymal  papillae  are  readily 
recognized  as  small  reddish  elevations  at  the  inner  angle  of 
the  upper  and  lower  eyelids.  The  lachrymal  canals  soon 
unite,  opening  into  the  nasal  duct,  the  upper  portion  of 
which  is  somewhat  enlarged  and  called  the  lachrymal  sac. 
The  lower  portion  of  the  nasal  duct  opens  into  the  back 
part  of  the  nose  chamber,  and  from  this  place  the  tears  find 
their  way  into  the  throat  and  are  swallowed.  Ordinarily  the 
amount  of  the  secretion  so  poured  into  the  throat  is  so  slight 
that  we  take  no  notice  of  it.  In  violent  weeping,  however, 
the  secretion  may  become  so  plentiful  as  to  necessitate  re- 
peated acts  of  swallowing. 

4. — The  Muscles  of  the  Eyeball.  The  rapidity  and  ex- 
actness with  which  the  eyeball  may  be  moved  attest  the 
presence  of  a  system  of  eye  muscles.  Each  globe  is  pro- 
vided with  six  muscles ;  four  of  these  are  straight  muscles 
and  two  are  oblique.  The  straight  muscles  lie,  one  on  top 
of  the  eye — the  superior  rectus,  one  below  the  eyeball, 
the  inferior  rectus,  one  on  the  outer  side  —  external  rec- 
tus, and  the  fourth  on  the  inner  side  —  internal  rectus. 
It  is  readily  seen  that  by  means  of  these  four  muscles  the 
globe  of  the  eye  may  be  turned  in  any  direction  save  a 
rotary  one.  To  make  this  motion  possible  there  are  two 
oblique  muscles.  One  of  these  is  fastened  to  the  top  of  the 
eyeball,  runs  inward  towards  the  nose,  and  there  passes 
through  a  tendonous  loop  like  a  pulley,  to  be  inserted  near 
where  the  recti  are.  This  is  the  superior  oblique  muscle. 
The  inferior  oblique  muscle  arises  at  the  back  of  the  orbit, 
near  the  lachrymal  sac.  From  this  point  it  passes  slightly 
outwards  and  backwards  beneath  the  eyeball,  and  is  inserted 


THE    EYE   AND   THE    PHYSIOLOGY   OF   VISION. 


545 


into  it  posteriorily.  The  exact  movements  which  each  of 
these  muscles  is  able  to  produce  may  be  readily  seen  from 
their  manner  of  attachment. 

One  of  the  most  striking  things  about  these  muscles  is 
the  harmony  with  which  they  work.  In  normal  eyes  the  co- 
ordination is  almost  perfect.  When,  however,  one  or  more 
of  these  muscles  cease  to  be  so  carefully  adjusted,  either  as 
a  cause  of  paralysis  or  of  other  causes,  there  results  what  is 
familiarly  called  the  "squint,'7  which  is  a  right  or  a  left,  an 
external  or  internal  squint,  according  to  the  muscle  affected. 
An  exaggerated  condition  of  a  squint  is  finally  termed 
"cross-eyed." 


Fig.  169.— SEMIDIAGRAMMATIC  SECTION  OF  THE  EYEBALL. 
(The  reader  will  find  the  explanation  of  the  section  in  the  text.) 

5. — The  Globe  of  the  Eye.     The  globe  of  the  eye  is  a 
spherical  body  an  inch  or  more  in  diameter,  with  a  large 
35 


546  STUDIES   IN   ADVANCED   PHYSIOLOGY. 

portion  of  it  visible  from  the  outside.  It  is  not  evenly 
spherical,  but  consists  of  segments  of  two  spheres,  the 
larger  sphere  composing  most  of  the  eyeball,  the  smaller 
sphere  forming  the  cornea. 

The  globe  is  a  completely  closed  ball  pierced  only  at  one 
end,  where  the  optic  nerve  and  the  blood-vessels  for  the 
retina  enter  it.  The  walls  are,  of  course,  provided  with 
blood-vessels  and  nerves  which  enter  it,  but  consist  almost 
wholly  of  very  tough  connective  tissue  so  strong  that  in  the 
case  of  a  beef's  eye  one  may  be  able  to  stand  on  an  eye 
without  breaking  these  coats. 

In  a  general  way  these  coats  are  described  as  consisting 
of  three,  called  the  outer  or  sclerotic  coat,  the  middle  or 
choroid  coat,  and  the  inner  coat  or  the  retina. 

Enclosed  within  these  coats  are  three  refracting  media; 
the  aqueous  humor,  the  crystalline  lens,  and  the  vitreous 
humor. 

6. — Sclerotic  Coat.  The  sclerotic  coat  is  the  outer  coat 
and  is  by  far  the  strongest  and  toughest.  It  consists  almost 
entirely  of  closely  packed  white  connective  tissue.  This 
coat  is  visible  from  the  outside  as  the  white  of  the  eye. 
Immediately  in  front  of  the  eyeball  this  coat  is  transparent 
and  is  called  the  cornea.  The  sphericity  of  the  cornea  is 
greater  than  that  of  the  eyeball  itself. 

The  sclerotic  coat  covers  the  entire  eye  save  at  the  back 
where  the  optic  nerve  and  the  retinal  blood-vessels  pass 
through  it.  The  cornea  is  covered  over  in  front  with  the 
conjunctiva,  and  on  its  inner  side  is  lined  with  a  layer  of  epi- 
thelial cells  called  the  membrane  of  Descemet. 

7. — The  Choroid  Coat.  Immediately  beneath  the  scle- 
rotic coat  is  the  choroid  coat.  This  is  not  nearly  so  tough 
as  the  sclerotic,  but  is  much  more  vascular  and  readily 
recognizable  in  the  dissection  of  the  eye  by  the  black  pig- 
ment which  it  contains.  It  is,  in  fact,  the  choroid  coat  to 
which  the  black  inner  walls  of  the  eyeball  are  due,  and  the 
presence  of  this  pigment  in  the  choroid  explains  largely  its 


THE    EYE    AND    THE    PHYSIOLOGY   OF   VISION.  547 

function.  All  good  optical  instruments  are  painted  black 
inside,  so  as  to  do  away  with  the  possibility  of  reflection 
from  the  walls,  which  would  materially  interfere  with  the 
clearness  of  the  image.  The  cornea  is  not  in  contact  with 
the  choroid,  but  at  this  point  the  sclerotic  coat  and  the 
choroid  are  separated  and  so  a  space  produced  which  is 
filled  with  a  watery  liquid  called  the  aqueous  humor.  The 
pigment  of  the  choroid  is  also  different  at  this  place,  and  in- 
stead of  being  black  is  brown  or  blue,  or  whatever  other 
color  we  find  the  eyes  to  have.  This  colored  portion  of  the 
choroid  coat  seen  through  the  cornea  is  called  the  iris. 

Just  in  the  middle  line  of  the  eyeball  the  iris  has  an 
opening  known  as  the  pupil,  and  visible  on  the  eye  as  a 
dark  disk  within  the  iris.  This  dark  disk  is  really  a  hole, 
but  seems  dark  because  no  light  conies  out  of  it,  just  as  an 
opening  into  a  mine  would  seem  dark  if  there  were  no  light 
beneath. 

Within  the  choroid  coat  lies  the  retina.  The  retina  is 
but  an  expansion  of  the  optic  nerve  and  does  not  run  en- 
tirely around  the  eye.  The  impossibility  of  throwing  an  im- 
age on  the  forward  portions  of  the  inner  wall  of  the  eye 
would  render  useless  the  extension  of  the  retina  so  far. 

Filling  the  large  posterior  chamber  is  the  vitreous 
humor,  a  transparent  glassy-looking  liquid  having  about 
the  consistency  of  the  white  of  an  egg.  This  vitreous 
humor  is  enclosed  in  a  delicate  membrane  extending  all 
around  it,  known  as  the  hyaloid  membrane.  This  mem- 
brane seems  a  single  layer  in  most  portions,  but  towards 
the  front  it  divides  into  two  layers,  and  in  the  space  so 
formed  there  is  imbedded  the  rather  large  crystalline  lens. 

As  the  eyeball  is  distended  even  to  a  slight  pressure 
with  the  vitreous  humor,  all  the  coats  are  held  in  place  and 
a  collapse  of  the  eyeball  is  prevented.  In  fact,  the  pressure 
of  the  vitreous  humor  in  the  hyaloid  membrane  is  normally 
such  as  to  stretch  this  somewhat,  and  as  the  lens  is  im- 
bedded between  the  layers  of  this  membrane  it  is  by  the 
stretching  of  this  hyaloid  membrane  always  in  a  state  of 


548  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

compression,  and  so  continually  flattened.  The  relation  of 
this  fact  to  the  power  of  accommodation  will  be  evident  a 
little  further  on. 

That  part  of  the  hyaloid  membrane  which  immediately 
surrounds  the  lens  is  called  the  capsule  of  the  lens,  while 
that  next  to  the  capsule  of  the  lens  is  spoken  of  as  the  sus- 
pensory ligament. 

8. — Ciliary  Muscles  and  the  Muscles  of  Accommodation. 
There  occur  in  the  iris  two  sets  of  muscles ;  a  circular  set 
by  the  contraction  of  which  the  pupil  is  made  smaller,  and 
a  radial  set,  the  contraction  of  which  causes  an  increase  in 
the  opening  of  the  pupil.  In  addition  to  these  muscles  of 
the  iris  there  are  found  imbedded  in  the  choroid  coat  just  at 
the  point  where  the  choroid  coat  and  the  cornea  meet,  a 
system  of  muscles  known  as  the  muscles  of  accommoda- 
tion. These  muscles  are  attached  firmly  at  one  end  where 
the  cornea  and  the  choroid  unite,  from  which  point  they  ex- 
tend backwards  through  the  choroid  in  such  a  way  that  when 
they  contract  they  pull  the  choroid  coat  forward  towards  the 
cornea.  It  will  be  pointed  out  that  by  means  of  these  mus- 
cles the  eye  is  focussed  for  far  and  near.  At  the  point 
where  the  cornea  and  the  iris  meet  there  is  a  small  canal 
running  around  the  eye,  called  the  canal  of  Schlemm.  Be- 
tween the  two  layers  of  the  hyaloid  membrane  where  they 
separate  to  enclose  the  lens  there  is  a  second  canal  en- 
circling the  lens  called  the  canal  of  Petit.  Between  the 
suspensory  ligament  and  the  iris  there  is  usually  a  small 
space  which  is  but  a  continuation  of  the  space  containing 
the  aqueous  humor.  This  space  is  called  the  posterior 
chamber  of  the  aqueous  humor. 

Reference  to  the  diagram  of  the  eyeball  will  show  its 
close  analogy  to  a  camera,  in  which  the  refracting  media 
are  the  cornea,  the  lens  and  the  humors.  The  image  will 
fall  on  the  retina,  and  as  the  light  usually  enters  the  eye  in 
a  certain  straight  direction  the  image  will  regularly  fall 
straight  behind  the  lens.  This  point  on  the  retina  where 
the  most  acute  vision  occurs  is  called  the  yclloiv  spot.  It 


THE    EYE   AND   THE    PHYSIOLOGY   OF   VISION.  549 

is  visible  on  the  retina  as  a  yellowish  depression.  When 
we  wish  to  see  objects  in  detail,  such,  for  instance,  as  the 
print  on  a  page,  we  allow  the  image  to  fall  on  this  yellow 
spot.  Images  which  fall  on  other  portions  of  the  retina  are 
still  visible  but  not  distinctly  so.  At  the  spot  where  the 
optic  nerve  enters  the  eye  the  retina  has  no  sensitiveness  to 
light.  This  spot  is  called  the  blind  spot.  It  may  be  easily 
found  by  trying  the  experiment  suggested  in  Figure  170,  in 
which  the  cross  and  circle  are  so  arranged  that  when  one 
falls  on  the  yellow  spot  the  other  falls  on  the  blind  spot 
and  so  becomes  invisible.  The  blind  spot  is  sometimes 
called  the  optic  mound,  the  yellow  spot  the  macula  lutea, 
while  the  pit  in  its  center  is  called  the  fovea  centralis. 
The  retina  at  this  point  is  so  thin  that  the  black  choroid 
may  be  seen  shining  through  it. 


Fig.  170. — DIAGRAM  TO  DEMONSTRATE  THE  POSITION  OF  THE  BLIND  SPOT.  (Close  the  left 
eye,  and  holding  the  figure  about  a  distance  of  a  foot  from  the  face,  look  directly  at 
the  cross.) 

At  the  optic  mound  a  number  of  blood-vessels  which 
reach  the  eye  along  with  the  optic  nerve  spread  out  through 
the  retina  and  supply  this  coat  with  its  proper  nourishment. 

9. — The  Optic  Nerves.  In  the  chapter  on  nerves  atten- 
tion was  called  to  the  optic  nerves;  how  these  nerves  met 
in  the  optic  commissure  and  how  the  optic  tracts  passed 
from  this  point  to  the  midbrain  and  occipital  lobes.  It  was 
also  pointed  out  that  the  crossing  of  the  optic  nerves  at  the 
commissure  is  only  a  partial  one,  and  is  of  such  a  nature 


550  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

that  each  side  of  the  brain  controls  corresponding  halves 
of  the  retina,  so  that  the  loss  of  the  right  optic  tracts,  for 
instance,  would  result  in  blindness  of  the  left  halves  of 
both  retinas.  Of  course  if  the  optic  nerve  itself  were  cut 
then  the  entire  retina  to  which  it  went  would  become  blind. 

10. — The  Microscopic  Striicture  of  the  Retina.  In  order 
to  understand  the  physiology  of  the  eye  it  is  not  absolutely 
necessary  to  go  into  the  histological  structure  of  very  many 
of  its  parts.  An  exception  to  this,  however,  is  the  retina, 
which,  as  the  seat  of  vision,  has  an  exceedingly  delicate 
structure,  by  means  of  which  the  light  may  be  perceived. 
The  microscope  readily  reveals  ten  distinct  layers.  These 
are,  beginning  with  the  one  next  to  the  hyaloid  membrane, 
as  follows: 

First,  a  thin  transparent  membrane  called  the  internal 
limiting  membrane. 

Second,  a  nerve  fiber  layer  continuous  with  the  optic 
nerve  at  one  end  and  extending  further  into  the  retina  at 
the  other. 

Third,  the  nerve  cell  layer,  an  ordinary  ganglionic  layer 
with  which  the  nerves  of  the  second  layer  probably  connect. 

Fourth,  an  inner  molecular  layer  seen  to  consist  of  thin 
sections  of  very  small  granules,  which  granules,  however, 
are  probably  systems  of  dendrons  cut  across.  It  seems  prob- 
able that  this  molecular  layer  is  a  layer  in  which  the  dend- 
rons of  consecutive  neurons  meet.  This  is  succeeded  by, 

Fifth,  the  inner  nuclear  layer,  consisting  of  larger 
granules,  which  are  undoubtedly  small  nerve  cells,  so  that 
this  layer  may  be  looked  upon  as  a  second  ganglionic  layer. 
Next  to  this  is  found, 

Sixth,  the  outer  molecular  layer,  differing  from  the 
inner  molecular  layer  only  in  being  much  narrower.  This 
is  succeeded  by, 

Seventh,  the  outer  nuclear  layer  similar  in  construction 
to  the  inner  nuclear  layer  and  ganglionic  in  its  function. 
The  outer  nuclear  layer  is  bordered  by  a  very  thin  mem- 
brane called, 


THE    EYE    AND    THE    PHYSIOLOGY    OF   VISION. 


551 


Eighth,  the  external  limiting  membrane,  followed  by, 
Ninth,  the  rod  and  cone  layer,  the  layer  in  which  the 
actual  nervous  stimuli  arise.  As  the  name  indicates,  two 
kinds  of  structures  are  found  here,  somewhat  longer  and 
narrower  rods,  and  scattered  between  these  shorter  and 
thicker  cones.  These  rods  and  cones  project  into, 

Tenth,  the  pigment-cell  layer,  which  lies  in  contact  with 
the  choroid  just  beneath. 


Fig.  171.— DIAGRAMMATIC  REPRESENTATION  OF  THE  STRUCTURE  OF  THE  RETINA.    (After 

Y.  Cajal.) 

a,  layer  of  rods  S  and  cones  Z  Z\  F,  F,  fibers  of  Miiller;  A,  h,  external  limiting  mem- 
brane; b,  outer  nuclear  layer;  c,  outer  molecular  layer;  d,  inner  nuclear  layer;  e,  inner 
molecular  layer;  /,  nerve  cell  layer;  g,  nerve  fiber  layer;  k,  k,  internal  limiting  mem- 
brane. The  rods  are  composed  of  a  highly  refractive  end  portion  and  a  somewhat  more 
protoplasmic  basal  portion  which  then,  continued  through  the  cells  K  in  the  layer  &,  end 
in  the  layer  c  in  little  round  buttons.  Several  such  buttons  seem  in  turn  invested  by  the 
dendrons  of  a  single  cell  H  from  the  layer  d.  The  cones  also  have  a  refractive  terminal 
portion,  but  a  more  rounded  ellipsoid  basal  portion  of  protoplasmic  structure,  from  which 
a  relatively  large  fiber  at  once  passes  through  the  layer  b,  and  ending  in  dendrous  in  the 
layer  c,  invests  the  dendrons  of  a  single  cell  of  the  layer  d.  The  layer  d  contains  also 
cells  L,  which  run  outward  only,  and  cells  M,  which  send  dendrons  inward  only.  The 
superposition  of  neurons  is  quite  evident,  there  being  in  the  retina  itself  at  least  three 
such  superposed  units. 

Here  and  there  through  the  retina  may  be  seen  some- 
what stronger  fibers  reaching  from  the  internal  limiting 
membrane  as  far  as  the  rod  and  cone  layer.  They  serve 
probably  for  purposes  of  support  and  are  called  the  fibers 
of  Miiller.  The  meaning  of  the  layers  of  the  retina  will  be 
more  evident  by  reference  to  Figure  171,  which  is  a  diagram- 


552  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

matic  representation  of  the  relative  arrangement  of  these 
layers.  It  will  be  seen  that  the  retina  consists  of  a  number 
of  neurons,  the  cell  body  of  the  first  neuron  being  in  the 
third  layer.  From  these  large  cells  nerve  fibers  extend  in 
one  direction  along  the  optic  nerve  to  the  brain,  but  toward 
the  fourth  layer  are  given  off  short  dendrons  which  meet 
with  similar  dendrons  from  the  second  neurons,  the  cells  of 
which  lie  in  the  inner  nuclear  layer.  These  cells  send  their 
dendrons  into  the  sixth  layer  to  meet  similar  dendrons  be- 
longing to  neurons  whose  cells  lie  in  the  outer  nuclear 
layer. 

These  cells  extend  a  nerve  fiber  into  the  rod  and  cone 
layer.  In  fact,  the  rods  are  merely  special  terminations  of 
these  nerves.  The  cones  seem  to  be  partly  of  a  cellular  na- 
ture themselves,  which  connect  with  the  lower  neurons  in 
the  outer  molecular  layer  and  end  in  the  rod  and  cone  layer 
in  the  characteristic  points  found  on  these  cones. 

To  resume,  then,  the  retina  consists  of  three  systems  of 
neurons  super-imposed  one  above  the  other,  the  individual 
neurons  being  exceedingly  small,  but,  on  the  other  hand, 
exceedingly  numerous.  This  decrease  in  size  and  cor- 
responding increase  in  numbers  is  necessitated  by  the  deli- 
cacy which  the  retina  must  possess  to  be  affected  by  light 
and  so  make  possible  the  perception  of  two  points  of  light 
very  close  to  each  other.  The  touch  areas  for  light  in  the 
retina  must  be  very  much  smaller  indeed  than  the  touch 
areas  for  the  portions  of  the  skin  since  we  are  able  to  see 
two  points  of  light  which  are  separated  by  a  distance  meas- 
urable only  with  difficulty. 

A  somewhat  surprising  arrangement  of  the  retina  at  first 
sight  consists  in  the  relative  position  of  the  first  and  ninth 
layer.  Naturally  one  would  expect  to  see  the  rods  and 
cones  turned  towards  the  light.  In  reality  they  are  in  the 
human  eye,  as  in  the  eye  of  all  vertebrates,  turned  away 
from  the  light  and  the  light  has  to  permeate  the  eight 
super-imposed  layers  before  affecting  the  sensitive  rods  and 
cones.  This  inversion  of  the  retina  is  easily  understood 


THE   EYE    AND   THE    PHYSIOLOGY   OF   VISION.  553 

when  the  embryonic  development  of  the  eye  is  studied. 
Very  early  in  such  development  the  retina  can  be  seen  folded 
in  such  a  way  that  what  would  naturally  have  been  towards 
the  light  is  turned  away  from  the  light.  In  the  invertebrates 
the  rods  and  cones  turn  towards  the  light,  and  eyes  having 
such  an  arrangement  are,  therefore,  usually  referred  to  as 
invertebrate  eyes. 

THE  EYE  AS  A  PURELY  PHYSICAL  INSTRUMENT. 

The  ability  of  the  eye  to  bend  rays  of  light  passing 
through  its  refracting  media  and  to  produce  an  image  on  or 
near  the  retina  is  a  purely  physical  property.  Such  results 
would  occur  in  an  eye  that  had  been  removed  from  the 
body.  A  stimulation  of  the  rods  and  cones,  however,  and 
the  consequent  production  of  nervous  impulses,  which,  when 
reaching  the  brain  are  interpreted  as  color,  are  physiologi- 
cal processes  and  can  be  duplicated  in  no  artificially  con- 
structed instrument.  Before  proceeding  to  the  physiology 
of  the  eye  it  seems  desirable  to  call  attention  to  those  ar- 
rangements and  properties  which  it  shares  with  all  optical 
instruments,  and  to  the  defects  which  may  arise  in  the  eye 
in  common  with  other  optical  instruments. 

THE  NORMAL  OR  EMMETROPIC  EYE. 

When  the  eyeball  and  its  refracting  media  are  so  con- 
structed that  parallel  rays  of  light  shall  meet  in  a  focus  on 
the  retina  when  the  eye  is  in  a  resting  condition,  it  is  called 
a  normal  or  emmetropic  eye.  Rays  of  light  are  for  prac- 
tical purposes  considered  as  parallel  when  they  come  from 
a  point  removed  from  the  eye  about  twenty-five  feet  or  more. 
An  emmetropic  eye,  therefore,  may  be  defined  as  one  which 
in  its  natural  resting  position  is  in  focus  for  distant  objects. 
Many  eyes  do  not  conform  to  this  requirement,  but  show  in 
a  greater  or  less  degree  one  or  more  of  the  following  optical 
defects: 

1. — Myopia,  or  Short  Sight.  In  a  myopic  or  short- 
sighted eye  the  image  falls  in  front  of  the  retina,  produced 


554  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

by  either  one  or  both  of  the  following  causes:  (a)  The 
ball  may  be  too  long  from  before  backwards,  and  in  this  way 
the  retina  too  far  behind  the  lens  to  receive  the  image. 
Or,  (b)  the  lens  may  be  too  convex.  It  may  converge 
the  rays  of  light  too  much  and  so  bring  them  to  a  focus 
sooner  than  ought  to  have  been  done.  When  myopia  is  the 
result  of  a  long  eyeball  it  is  frequently  a  natural  defect. 
When,  however,  it  is  due  to  too  great  a  convexity  of  the 
lens  it  may  be  an  acquired  defect.  An  individual  who  has 
been  in  the  habit  of  looking  closely  at  things  held  very  near 
the  eye,  has  been  obliged  in  doing  so,  to  keep  his  lens 
strongly  curved,  and  the  continuation  of  such  a  state  of 
things  is  liable  to  finally  fix  itself  and  so  there  arises  short- 
sightedness, which  necessitates  that  all  objects  be  held  close 
to  the  eye  to  be  distinctly  visible. 

In  such  acquired  myopia  there  has  occurred  really  no  in- 
herent change  in  the  lens,  the  change  has  been  in  the  mus- 
cle itself,  which,  owing  to  its  constant  tension  in  looking 
closely,  has  finally  become  somewhat  fixed  in  this  position, 
and  by  this  fixation  of  the  muscle  the  lens  remains,  on  ac- 
count of  its  elasticity,  in  constant  excessive  convexity. 

The  remedy  for  short-sightedness  is  obvious.  As  the 
rays  of  light  are  bent  too  much  a  lens  must  be  placed  before 
the  eye  which  shall  disperse  them  to  such  an  extent  that  the 
image  shall  be  thrown  on  the  retina.  Concave  spectacles 
are  therefore  demanded,  the  extent  of  the  concavity  depend- 
ing upon  the  degree  of  myopia. 


a  ---• 


Fig.  172. — THE  MYOPIC  EYE  AND  ITS  CORRECTION. 

The  tendency  to  acquire  myopia  when  the  eye  is  re- 
peatedly subjected  to  a  close  strain  shows  the  necessity  de- 
volving upon  teacher  and  parent  to  prevent  the  habit  of 
reading  continuously  with  the  book  unnaturally  close.  It 


THE   EYE   AND   THE    PHYSIOLOGY   OF   VISION.  555 

is  an  element  of  optical  hygiene  to  insist  that  persons  with 
normal  eyes  to  begin  with  shall  hold  objects,  such  as  a 
printed  page,  at  a  reasonable  distance  from  the  eye. 

2. — Long  Sight  or  Hypermetropia.  Hypermetropia 
occurs  when  the  image  in  the  eye  would  naturally  fall  be- 
hind the  retina,  or  since  this  is  actually  impossible,  the 
real  state  of  things  is  the  absence  of  a  focus  altogether,  the 
rays  of  light  falling  on  the  retina  in  a  circle  before  they 
have  met  in  a  point.  The  causes  of  this  defect  are  two. 
(a)  It  may  consist  of  a  shortening  of  the  eyeball  from  be- 
fore backwards,  so  that  the  retina  now  is  in  front  of  its 
natural  position.  Or,  (£)  since  the  rays  of  light  are  not 
converged  enough  the  lens  may  be  too  nearly  flat.  The 
remedy  in  this  instance  is  equally  obvious.  The  converg- 
ing power  of  the  eye  must  be  increased,  and  so  convex 
glasses  are  needed. 

As  the  image  of  an  object  is  pushed  further  and  further 
back  in  the  eye  the  closer  the  object  itself  is  placed  to  the 
eye,  and  as  in  the  far-sighted  individual  this  shifting  of  the 
image,  backwards  exaggerates  the  difficulty,  such  persons 
have  a  clearer  vision  when  the  object  is  removed  some  dis- 
tance, whence,  of  course,  the  name  "far-sightedness." 


Fig.  173. — THE  HYPERMETROPIC  EYE,  AND  ITS  CORRECTION. 

It  is  well  to  point  out,  though,  that  in  many  cases  far- 
sighted  children  will  develop  a  habit  of  holding  the  book 
too  close  to  the  eye  and  so  leave  the  impression  on  the  ob- 
server that  they  are  near-sighted.  Such  a  far-sighted  child 
in  looking  at  the  page  before  him  does  not  see  it  distinctly, 
and  prompted  by  the  desire  to  look  more  closely  and  mis- 
led by  his  usually  correct  experience  that  approach  to  an 
object  increases  the  distinctness  of  its  vision,  he  moves  the 


556  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

page  closer  to  his  eye.  The  increase  in  the  intensity  oi  the 
light"  temporarily  increases  the  clearness,  but  the  difficulty 
is  soon  exaggerated  and  so  frequently  a  second  attempt  to 
see  more  clearly  is  made  by  moving  the  object  still  closer. 
Teachers  especially  should  be  on  the  lookout  for  such  cases 
since  the  confounding  of  far-sight  with  near-sight  might 
lead  to  undesirable  results.  Far-sightedness  also  very  gen- 
erally induces  inflamed  conditions  of  eyes  and  eyelids,  and 
seems  a  predisposing  cause  in  the  production  of  styes. 

3. — Astigmatism.  The  distinctness  of  an  object,  as  any 
one  will  readily  understand  who  has  handled  lenses  of  any 
kind,  depends  upon  an  even  curvature  and  density  of  the 
lens  in  question.  If  the  surface  of  a  lens  be  made  un- 
even, a  greater  or  less  distortion  of  the  image  occurs.  If, 
for  instance,  a  drop  of  water  is  allowed  to  run  across  the 
front  of  a  pair  of  spectacles,  objects  seen  through  them  are 
at  once  distorted.  The  water  in  this  case  having  about  the 
same  density  as  glass,  acts  really  like  a  bit  of  extra  glass 
put  on  the  spectacles,  and  so  the  surface  of  it  is  made  un- 
even. The  spectacles  under  these  circumstances  are  astig- 
matic. 

Exaggerated  cases  of  astigmatism  are  also  observable  on 
nearly  all  window  panes,  for  seldom  (except  in  the  case  of 
plate  glass)  is  a  window  pane  so  even  as  not  to  distort  the 
objects  seen  through  it,  while  sometimes  the  distortion  is 
so  great  as  to  transform  a  straight  object  seen  through  it 
into  a  series  of  zig-zags. 

It  is  not  necessary  that  a  lens  should  have  such  exagger- 
ated cases  of  unevenness  to  be  astigmatic.  It  may,  in  fact, 
be  quite  smooth,  but  if  the  curvature  in  one  direction  differs 
from  the  curvature  in  another  direction,  a  distortion  or  rela- 
tive change  of  focus  for  the  various  parts  of  the  lens  will 
arise.  Rays  of  light  passing  through  the  lens  where  it  has 
a  greater  curvature  will  come  to  a  focus  sooner  than  rays 
of  light  passing  through  portions  of  a  lens  having  a  lesser 
curvature. 


THE    EYE    AND    THE    PHYSIOLOGY   OF   VISION.  557 

Applying  this  to  the  eye  we  find  that  it  not  infrequently 
occurs  that  a  cornea  possesses  such  irregularities  of  curva- 
ture, and  astigmatism  is  the  result.  The  presence  of  as- 
tigmatism can  be  readily  detected  by  looking  at  a  disk  on 
which  are  placed  the  numerals  arranged  like  those  on  the 
face  of  a  clock.  Astigmatic  persons  will  see  some  of  these 
numerals  in  focus,  while  others  are  indistinct  and  blurred. 
When  the  focus  is  changed  to  the  blurred  ones  and  these 
become  distinct,  the  first  become  blurred.  Or  if  one  look  at 
a  system  of  concentric  rings,  such  as  given  in  Figure  174, 
astigmatic  persons  will  perceive  certain  sectors  in  which  the 
lines  are  blacker  and  more  distinct,  bordered  by  portions 
where  they  are  blurred  and  indistinct. 


Fig.  174. — FIGURES  TO  DEMONSTRATE  THE  EXISTENCE  OF  ASTIGMATISM. 

To  remedy  astigmatism  it  is  necessary  to  grind  a  special 
lens  of  such  a  form  that  it  shall  exactly  counteract  the  in- 
distinctness of  the  cornea,  the  lens  being  more  rounded 
where  the  cornea  is  not  rounded  enough,  and  hollowed  out 
where  the  cornea  possesses  too  much  curvature.  The  fit- 
ting of  a  lens  for  astigmatism  must  in  each  case  be  a  bit  of 
special  work,  there  being  possibly  no  two  cases  of  astig- 
matism exactly  alike. 

4. — Cataract.  Cataract  is  an  optical  defect  arising 
from  the  opacity  of  the  lens.  When  light  is  no  longer 
able  to  penetrate  this  readily,  a  more  or  less  complete 
blindness  results,  the  only  remedy  for  which  is  the  removal 
of  the  lens  from  the  eye  and  the  substitution  for  it  of  an 
artificial  lens  in  front  of  the  eye. 

In  addition  to  the  usual  cataracts  of  the  lens,  there 
occur  sometimes  slight  opacities  in  the  cornea. 


558  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

5. — Spherical  Aberration.  Spherical  aberration  is  not 
so  much  .a  real  defect  of  the  eye  as  it  is  a  somewhat  uni- 
versal defect  of  all  lenses,  and  it  is  therefore  in  common 
with  all  lenses  shared  by  the  crystalline  lens.  All  the  rays 
of  light  passing  through  a  lens  do  not  meet  at  the  same 
point,  but  the  rays  of  light  passing  near  the  edge  of  the 
lens  are  brought  to  a  focus  sooner  than  those  passing  nearer 
the  middle,  and  consequently  when  the  edge  of  the  lens  is 
in  focus  the  center  is  blurred,  and  vice  versa.  Instances  of 
such  spherical  aberration  are  frequently  noticeable  on  or- 
dinary opera-glasses,  where  when  objects  seen  through  the 
middle  of  the  lens  are  in  focus  the  field  around  the  edge  of 
the  lens  seems  blurred.  There  would  be  two  ways  to  remedy 
this  defect.  One  to  cut  the  light  out  of  the  edge  of  the  lens 
by  placing  a  circular  shutter  over  it.  Such  is,  in  fact,  very 
usual  in  optical  instruments,  and  photographers  frequently 
interpolate  a  shutter  having  a  small  hole  in  it  through 
which  the  light  is  able  to  reach  the  center  of  the  lens  only. 
A  similar  arrangement  exists  in  the  eye  where  the  iris  cuts 
off  the  entire  outer  portion  of  the  crystalline  lens  and  per- 
mits the  light  passing  through  the  pupil  to  reach  the  cen- 
ter of  the  lens  only.  V 

A  second  way  to  remedy  spherical  aberration  would  be 
to  increase  somewhat  the  density  of  the  middle  of  the  lens, 
for  as  the  rays  of  light  passing  through  the  edge  of  the  lens 
are  bent  more  an  increase  of  the  density  of  the  middle  of  the 
lens  would  bend  the  rays  passing  through  it  more,  and  so 
the  foci  would  coincide.  Both  of  these  plans  are  followed 
in  the  eye,  the  function  of  the  iris  having  just  been  pointed 
out,  and  in  addition  to  this  the  lens  has  a  slightly  greater 
density  in  the  middle,  the  result  of  these  two  agencies  being 
to  reduce  this  defect  in  most  eyes  to  an  imperceptible  mini- 
mum. 

6. — Chromatic  Aberration.  A  second  almost  universal 
defect  of  lenses  is  chromatic  aberration.  This  defect  arises 
from  the  unequal  refraction  which  the  different  colors  suffer 
while  passing  through  a  lens.  It  will  be  remembered  that  the 


THE   EYE   AND   THE    PHYSIOLOGY   OF   VISION.  559 

formation  of  a  spectrum  is  the  result  of  such  an  unequal 
bending,  the  red  rays  being  bent  least,  the  violet  rays  most. 
Evidently,  therefore,  since  white  light  is  composed  of  the 
seven  fundamental  colors,  the  violet  rays  being  bent  more 
than  the  red  rays  will  come  to  a  focus  sooner,  and  in  this 
way  there  will  be  produced  a  number  of  foci  corresponding 
to  the  number  of  different  colors,  and  objects  will  appear 
violet,  greenish,  or  red,  according  as  the  violet,  green,  or 
red  focus  falls  on  the  retina. 


Fig.  175. — DIAGRAM  TO  ILLUSTRATE  THE  CHROMATIC  ABERRATION  OF  THE  EYE. 
r,  r',  red  rays;  t?,  »',  violet  rays;  V,  violet  focus;  B,  red  focus;  m,  n,  position  of  image 
with  a  red  border;  p,  s,  position  of  image  with  a  violet  border. 

This  chromatic  aberration  is  most  marked  near  the  edge 
of  a  lens,  and  a  peep  through  most  opera-glasses  shows  this 
defect  very  plainly.  While  the  center  of  the  field  is  plain 
white,  the  edge  of  the  field  is  tinted  with  some  color  due  to 
chromatic  aberration.  This  defect  is  reduced  to  an  almost 
imperceptible  minimum  in  the  human  eye  by  the  exclusion 
of  the  light  through  the  edge  of  the  lens. 

7. — Muscae-Volitantes.  While  the  humors  of  the  eye 
are  practically  quite  transparent  there  occur  not  infrequently 
small  opaque  particles  floating  in  them,  the  shadow  of  which 
is  by  the  light  entering  the  pupil  thrown  against  the  retina 
and  there  perceived  as  a  more  or  less  black  object,  which  by 
the  mind  is  projected  out  into  space.  These  are  the  flying 
motes.  These  opaque  particles  are  remnants  of  embryonic 
blood-vessels  in  the  humor. 

8. — Presbyopia.  As  the  name  indicates,  this  is  a  disease 
which  arises  usually  in  advancing  age.  The  ability  to  focus 


560  STUDIES    IN    ADVANCED    PHYSIOLOGY, 

the  eye  depends  upon  the  elasticity  of  the  lens.  But  this 
elasticity  becomes  gradually  reduced  and  in  old  age  fre- 
quently disappears  altogether.  Such  persons  are  unable  to 
accommodate  their  eyes  for  far  and  near,  a  defect  familiarly 
called  old-sight. 

To  remedy  this  it  is  obvious  that  several  pairs  of  lenses 
are  required  to  adjust  the  eye  to  several  distances.  Such 
persons  will  not  infrequently  have  one  system  of  lenses  for 
far  objects,  a  second  system  for  relatively  near  objects,  the 
objects  in  a  room,  for  instance,  and  a  third  system  to  be 
pressed  into  service  in  such  acts  of  vision  as  the  reading  of 
a  printed  page. 

THE  MANIPULATION  OF  THE  ETE  AS  AN  OPTICAL  INSTRUMENT. 

Every  optical  instrument  must  have  some  arrangement 
by  means  of  which  it  can  be  focussed.  In  the  photograph 
camera  this  focussing  consists  in  moving  the  lens  forward 
or  backward,  or  in  changing  the  relative  position  of  the 
sensitive  plate  behind  the  lens.  The  microscope  is  focussed 
by  lifting  the  tube  of  the  microscope  or  dropping  it  closer 
to  the  object  on  the  stage.  In  the  telescope  the  focus  is 
produced  by  shifting  the  relative  positions  of  the  lenses. 
Evidently  there  must  be  in  the  eye  some  arrangement  by 
means  of  which  it,  also,  may  be  focussed. 

That  such  is  the  case  is  the  commonest  experience  of 
every-day  life.  We  are  conscious  of  a  change  in  the  eye 
when  we  turn  our  view  from  a  distant  object  to  one  close 
by,  and  this  change  in  the  eye  is  independent  of  any  move- 
ment of  the  eyeball.  We  may  close  one  eye  and  then  look 
at  two  points  lying  in  the  same  direction  so  that  there  is  no 
turning  of  the  eyeball,  and  yet  a  change  from  the  focus  of 
one  to  the  focus  of  the  other  is  a  clearly  perceivable  one. 
This  change  in  the  eye  is  called  the  accommodation  of  the 
eye,  and  the  question  arises,  how  this  is  brought  about. 

HOW  DO  WE  FOCUS  THE  EYE  f 

It  is  at  once  out  of  the  question  to  think  this  is  brought 
about  by  a  lengthening  of  the  eyeball,  like  a  camera,  or  the 


THE   EYE   AND   THE    PHYSIOLOGY   OF   VISION.  561 

shifting  of  the  position  of  the  retina,  as  in  the  telescope, 
and  surely  the  lens  cannot  move  from  the  position  in  which 
it  is  so  firmly  held  by  the  suspensory  ligament.  The 
change  of  focus  is  produced  by  a  change  in  the  curvature 
of  the  lens.  That  this  is  true  may  be  easily  demonstrated 
by  the  following  experiment:  If  with  suitable  apparatus 
one  observe  the  images  reflected  out  of  the  eye  it  is  not  at  all 
difficult  to  notice  three  such.  A  very  clear  reflection  from 
the  front  of  the  cornea,  a  second  image  reflected  from  the 
front  of  the  lens,  and  a  third  image  from  the  posterior  sur- 
face of  the  lens.  If  these  three  surfaces  remain  in  the  same 
position  the  relative  positions  of  the  images  will  remain,  but 
if  one  or  more  of  these  surfaces  should  change  in  any  way, 
the  relative  position  and  sizes  of  these  images  would  vary. 
If,  now,  a  person  from  whose  eyes  such  images  are  reflected 
be  asked  to  focus  his  eye  for  a  distant  object,  and  the  posi- 
tion of  the  images  noted,  and  the  person  be  then  asked  to 
change  the  focus  to  a  near  object,  two  of  the  images  change. 
The  image  from  the  front  of  the  cornea  is  unaffected,  show- 
ing that  the  cornea  lias  remained  stationary.  The  image 
from  the  back  margin  of  the  lens  changes  just  a  little,  in 
such  a  way  as  to  show  that  this  surface  has  become  more 
convex.  The  greatest  change  occurs  to  the  image  reflected 
from  the  front  of  the  lens.  This  moves  much  more  rela- 


a,     6      # 

Fig.  176.— THE  REFLECTIONS  OF  TWO  BRIGHT  SQUARES  FROM  THE  CORNEA,  FRONT  AND 

BACK    OF    LENS,   A    IN  REST;   B  WHEN  THE  EYE  IS  ACCOMMODATED  FOR  A  NEAR  OB- 
JECT.    THE  IMAGES  a,  a,  FROM  CORNEA  DO  NOT  CHANGE,  NOR  DO  THOSE  c,  c,  FROM 

BACK    OF    LENS,   BUT    6    IN    FIGURE  23  IS  MUCH   SMALLER,    SHOWING   AN  INCREASE  IN 
THE   CONVEXITY   OK  THE  FRONT   OF   LENS. 

lively  and  shows  that  the  front  of  the  lens  has  been  pushed 
forward  and  become  much  more  rounded.      A  clearer  proof 
36 


562  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

of  the  change  of  form  of  lens  in  the  accommodation  of  the 
eye  cannot  be  desired. 

This  change  also  accords  with  what  we  know  of  the 
property  of  lenses.  We  know,  for  instance,  that  when  an 
object  is  moved  closer  to  a  lens  the  image  which  the  lens 
forms  is  pushed  further  back,  and  if  this  pushing  back  is 
not  desired  the  rays  of  light  must  be  bent  more;  that  is, 
brought  to  a  focus  sooner,  a  result  easily  produced  by  in- 
creasing the  convexity  of  the  lens.  The  problem,  there- 
fore, narrows  itself  down  to  the  explanation  of  the  manner 
in  which  this  change  of  lens  is  brought  about.  The  first 
element  of  this  explanation  is  found  in  the  elasticity  of  the 
lens.  It  is  a  quite  elastic  structure  made  up  of  almost  trans- 
parent cells,  and  is  in  its  usual  position  continually  unnatu- 
rally flattened.  This  is  proved  by  seeing  that  when  the  lens 
is  removed  from  the  eye  it  at  once  becomes  more  nearly 
round  than  before.  It  is  flattened  in  spite  of  its  elasticity 
by  the  pull  which  the  capsule  of  the  hyaloid  membrane 
exerts  upon  it,  and  this  pull  is  brought  about  by  the  pres- 
sure of  the  vitreous  humor  which  it  exerts  upon  the  hyaloid 
membrane  around  it.  The  lens  is  flattened  out  much  like 
a  foot-ball  would  be  flattened  out  if  it  should  be  put  under 
a  person's  coat  and  the  individual  should  then  distend  his 
lungs  with  air.  To  make  the  analogy  more  complete  we 
might  imagine  the  foot-ball  placed  between  the  outer  cloth 
of  the  coat  and  the  lining,  and  the  coat  then  buttoned  up. 
If  now  the  chest  were  expanded,  as  the  vitreous  humor  ex- 
pands the  hyaloid  membrane,  the  foot-ball  would  be  mate- 
rially flattened.  Thus,  to  repeat,  in  the  natural  resting 
condition  of  the  eye  the  lens  is  flattened,  and  if  the  eye  be 
a  normal  one,  therefore  adjusted  to  far  objects.  An  in- 
crease in  the  convexity  of  the  lens  is  brought  about  by 
producing  a  slack  in  the  capsule  and  suspensory  ligament 
surrounding  the  lens.  This  slack  is  produced  by  the  action 
of  the  ciliary  muscles  already  described.  These,  it  will  be 
remembered,  are  muscles  imbedded  in  the  choroid  coat,  one 
end  fixed  to  the  point  where  the  choroid  coat  is  firmly 


THE   EYE   AND   THE    PHYSIOLOGY   OF   VISION. 


563 


attached  to  the  sclerotic  coat,  the  other  ending  loosely  in 
the  choroid  coat  where  this  runs  backward  around  the  eye- 
ball. It  is  evident  that  when  these  ciliary  muscles  contract 
they  will  tend  to  pull  the  choroid  coat  forward;  that  is, 
towards  the  lens.  As  the  hyaloid  membrane  lies  immedi- 
ately underneath  the  choroid  coat  it  will  be  pulled  forward 
along  with  the  choroid  coat  and  so  thereby  produce  a  slack- 
ening of  the  tension  of  the  hyaloid  membrane,  where  it 
encloses  the  lens.  As  soon  as  the  slack  is  produced,  the  lens 
by  its  inherent  elasticity  becomes  more  rounded,  and  by  its 
increased  convexity  the  focus  of  the  eye  is  changed  for  a  new 
distance.  To  maintain  this  focus  it  is  evident  that  the  cil- 
iary muscles  must  remain  contracted  and  keep  this  slack, 
for  as  soon  as  the  ciliary  muscles  relax  the  choroid  coat  and 
the  hyaloid  membrane  with  it  move  back  to  their  original 
position  under  the  pressure  of  the  vitreous  humor  inside. 


Fig.   177.— TO    SHOW  THE    RELATIVE  SHAPES  OF  LENS  WHEN  AT  REST    (LEFT  HALF)   AND 
WHEN  ACCOMMODATED  FOR  NEAR  OBJECTS   (RIGHT  HALF). 

For  explanation  of  other  structures  see  the  text. 

To  recur  to  the  analogy  above,  let  us  imagine  the  foot- 
ball between  the  cloth  and  the  lining  of  the  coat.  The  coat 
represents,  therefore,  the  hyaloid  membrane.  To  represent 
the  choroid  coat  around  this  hyaloid  membrane  imagine  an 
overcoat  put  over  the  coat.  It  will  be  readily  seen  that  if 
the  overcoat  could  by  means  of  the  hands  or  any  agency  be 
pulled  forwards  towards  the  chest,  it  would  tend  to  pull  the 


564  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

coat  underneath  it  with  it,  and  there  would  be  produced  in 
the  coat  a  slack  over  the  chest.  The  elastic  foot-ball  im- 
bedded in  the  coat  would  at  once  take  advantage  of  this 
slack  and  try  to  return  to  its  natural  round  position.  As 
soon  as  the  forward  pull  on  the  sides  of  the  overcoat 
ceased,  the  overcoat  and  the  coat  underneath  it  would  fall 
back  to  their  natural  position  under  the  regular  pressure  of 
the  enclosed  body.  Accommodation  is  thus  the  product  of 
two  factors:  first,  the  pulling  forward  of  the  choroid  coat 
and  with  it  the  hyaloid  membrane  next  to  it,  and  the  conse- 
quent production  of  a  slack  of  the  suspensory  ligament  and 
capsule.  Second,  the  elasticity  of  the  lens  which  enables  it 
to  take  advantage  of  this  slack  to  return,  to  some  extent  at 
least,  to  its  more  rounded  form.  Hither  the  paralysis  of  the 
muscles  or  the  loss  of  elasticity  of  the  lens  would  at  once 
make  the  accommodation  of  the  eye  impossible. 

This  explanation  is  the  one  advanced  by  Helmholtz,  and 
is  the  one  which  is  now  almost  universally  accepted  as  cor- 
rect. Recently  there  has  been  advanced,  on  not  very  good 
grounds,  however,  a  second  explanation.  According  to 
this  second  explanation  the  increase  in  the  convexity  of  the 
lens  is  brought  about  by  the  contraction  of  some  circular 
fibers  which  seem  to  lie  among  the  radial  fibers  of  the  cili- 
ary muscles,  by  the  contraction  of  which  circular  fibers  the 
lens  is  rounded.  As  these  circular  fibers  are  said  to  sur- 
round the  lens  like  a  rubber  band,  it  is  clear  how  a  flat- 
tened object  would  have  its  convexity  increased  by  a 
circular  pressure  exerted  upon  it  in  the  manner  indicated, 
but  as  most  of  the  fibers  of  the  ciliary  muscles  are  radial 
fibers,  and  as  even  the  few  circular  fibers  do  not  lie  suf- 
ficiently close  to  the  margin  of  the  lens,  this  explanation 
does  not  seem  satisfactory,  especially  so  in  view  of  the 
completeness  of  the  other  explanation. 

It  will  be  remembered  in  the  chapter  on  the  distribu- 
tion of  nerves  that  the  ciliary  muscles  are  innervated  with 
branches  from  the  oculi  motores. 

With  the  process  of  accommodation  are  associated 
changes  in  the  size  of  the  pupil.  The  enlarging  of  the 


THE    EYE   AND   THE    PHYSIOLOGY   OF   VISION.  565 

pupil  is  accomplished  by  the  radial  fibers  of  the  iris,  its 
contraction  by  the  circular  ones.  The  pupil  changes  its 
caliber  under  the  following  circumstances: 

First.  Very  strong  light  thrown  into  the  eye  causes  a 
contraction  of  both  pupils,  even  when  the  strong  light  is 
admitted  to  one  eye  only. 

Second.  Under  a  constant  light  the  pupil  contracts 
when  the  eye  is  accommodated  for  objects  near  by. 

Third.  A  contraction  of  the  pupil  seems  to  accompany 
the  movements  of  the  eyes  inwards.  This  is  probably  but 
a  special  case  of  number  two,  as  ordinarily  the  eyes  are 
turned  inward  when  they  are  accommodated  for  near  ob- 
jects. 

Fourth.    The  pupil  is  contracted  in  sleep. 

Fifth.  The  pupil  is  much  dilated  in  cases  of  asphyxia- 
tion. A  dilation  also  usually  follows  a  strong  stimulation 
of  any  large  region  of  the  skin  of  the  body. 

Sixth.  Various  drugs  have  a  decided  effect  upon  the 
pupil.  Thus,  atropin  and  belladonna  dilate  the  pupil, 
while  nicotine  and  morphine  cause  it  to  contract. 

THE  DIOPTRICS  OF  THE  ETE. 

In  a  general  way  the  passage  of  rays  of  light  through 
the  media  of  the  eye  has  been  pointed  out,  and  while  it 
would  be  out  of  place  here  to  go  into  the  detailed  mathe- 
matical considerations  of  the  various  foci  and  indices  of  re- 
fraction a  few  elementary  considerations  of  this  nature  seem 
appropriate.  Although  the  eye  consists  of  several  refract- 
ing media,  these  three  media  may  mathematically  be  re- 
solved into  one,  and  the  cardinal  points  for  such  a  com- 
posite medium  be  determined.  In  Figure  178  the  line  // 
actually  indicates  the  curvature  of  a  lens  of  the  density  of 
the  vitreous  humor  which  would  have  the  same  refracting 
power  as  the  entire  eye.  To  determine  at  what  point  on 
the  retina  the  refracting  media  of  the  eye  will  throw  an 
image  it  is  necessary  that  several  determining  points  of 
these  media  be  established.  These  have,  with  considerable 


566 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


accuracy,  been  made  out  on  the  human  eye  and  are  given 
approximately  correct  in  Figure  178. 

It  will  be  noticed  that  in  the  lens  itself  not  far  from  its 
posterior  portion  there  are  indicated  two  points  marked  k' 
and  k".  These  are  called  the  nodal  points  of  the  eye.  A 
ray  of  light  entering  in  any  direction  through  the  pupil  and 
passing  through  point  k'  will  proceed  from  k'  to  k",  and  at 
k"  be  bent  parallel  to  its  direction  of  entrance.  As,. how- 
ever, for  practical  purposes  k'  and  k"  are  very  close  to- 
gether we  may  imagine  them  as  one  point,  and  that  any  ray 
of  light  which  passes  through  k'  will  be  continued  to  the 
retina  without  suffering  any  bending 


Fig.  178. — SEMI-DIAGRAMMATIC  SECTION  OK  THE  EYE-BALL. 
The  explanation  of  lines  and  letters  is  given  in  the  text. 

To  know,  therefore,  where  on  the  retina  a  certain  lum- 
inous point  will  be  imaged,  it  is  necessary  to  draw  a  straight 


THE:    EYE   AND   THE    PHYSIOLOGY   OF   VISION.  567 

line  from  the  luminous  point  in  question  through  the  nodal 
point  of  the  eye  to  the  retina.  If  the  eye  be  a  normal  one 
and  focussed  properly  all  the  other  rays  of  light  from  this 
same  luminous  point  will  fall  at  the  same  point  on  the  retina 
as  the  straight  unbent  one  passing  through  the  nodal  point. 

In  Figure  178  two  directions  of  light  are  indicated. 
One,  F'  F"  passes  through  the  horizontal  axis  of  the  eye, 
and  passing  through  the  point  k'  k"  suffers  no  bending. 
The  line  G'  G"  is  a  second  direction  of  light  passing 
through  the  point  k'  k"  and  so  is  continued  straight  back 
to  the  retina. 

The  line  of  light  G'  G''  is  the  common  path  of  light  fall- 
ing on  the  yellow  spot.  It  is  apparent,  therefore,  that  the 
geometric  axis  of  the  eye  is  not  the  path  which  the  light 
usually  takes  in  entering  it,  but  that  the  yellow  spot  is 
slightly  above  the  axis,  thus  necessitating  in  ordinary  vision 
a  constant,  although  slight  rotation  of  the  eyeball  upwards. 

It  may  be  pointed  out  once  more  that  all  the  refracting 
media  of  the  eye  reduced  to  a  single  medium  would  in  its 
optical  action  be  that  of  a  spherical  surface  of  vitreous 
humor  of  a  little  over  5  mm.  radius,  as  indicated  by  the 
line  //  in  the  figure,  which  surface  would  have  as  its  central 
point  the  nodal  point  indicated  by  the  letter  H". 

THE  LUMINOSITY  OF  EYES. 

On  account  of  the  black  choroid  which  lines  the  inside 
of  the  eye,  very  little  light  indeed  is  reflected  back  out  of 
the  eye,  it  being  all  absorbed  by  this  coat.  For  this  reason 
the  pupil  looks  black.  It  is  true,  though,  that  even  in  the 
human  eye  a  little  light  is  reflected  out  of  the  pupil,  enabling 
an  observer  by  means  of  proper  instruments  to  see  the 
retina.  In  many  of  the  lower  animals,  on  the  other  hand, 
a  very  much  increased  amount  of  light  is  reflected  through 
the  pupil,  sometimes  to  such  an  extent  as  to  make  the  eyes 
luminous,  as  for  instance,  those  of  a  dog,  cat,  or  tiger. 
This  is  brought  about  by  the  presence  of  a  reflecting  mem- 
brane in  the  back  of  the  eyes  of  these  animals,  called  the 


568  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

tapetum.  This  luminosity  of  the  eyes  is  most  readily  ob- 
servable if  such  an  animal  be  placed  in  a  darkened  room 
and  light  admitted  through  a  door  in  which  the  observer 
himself  stands.  In  that  case  it  is  frequently  possible  to  see 
the  two  eyes  luminous  enough  to  shine  in  the  dark,  the  ex- 
planation being,  as  just  pointed  out,  the  light  which  is 
actually  reflected  out  of  the  eye  by  the  shining  tapetum 
within. 

THE  PHYSIOLOGY  OF  COLOR  SENSATION. 

Up  to  this  point  the  eye  has  been  treated  almost  exclu- 
sively as  a  purely  physical  instrument,  unless  we  except  the 
nerves  and  muscles  by  means  of  which  it  accommodates 
itself.  But  all  these  physical  arrangements  in  the  eye  are 
intended  to  make  possible  the  physiological  perception  of 
color  in  the  retina.  It  has  been  pointed  out  how  the  image 
is  spread  upon  the  retina,  and  there  arises  now  the  question 
how  this  physical  image  is  translated  into  physiological 
phenomena.  In  other  words,  how  do  we  see  colors? 

It  is  well  to  note  that  it  is  color  and  color  alone  that  we 
observe  with  the  eyes.  Distance,  solidity,  form,  size,  etc. ,  are 
all  inferences  which  we  draw  from  the  arrangement  of  colors 
before  us.  The  eye  sees  color  or  absence  of  color,  and  ar- 
rangement of  colors,  and  nothing  more. 

The  physiology  of  vision  pure  and  simple,  therefore, 
narrows  itself  down  to  the  perception  of  these  colors.  Un- 
fortunately we  are  yet  far  removed  from  a  complete  under- 
standing of  this  question,  and  the  theories  that  have  been 
advanced  have  left  so  much  still  unexplained  that  they  have 
scarcely  the  dignity  of  scientific  theories.  They  are,  how- 
ever, the  best  attempts,  in  the  light  of  what  we  now  know, 
towards  the  explanation  of  these  phenomena. 

Two  fairly  distinct  theories  are  proposed.  These  are 
the  Young-Helmholtz  theory,  as  suggested  by  Young  early 
in  this  century,  and  later  on  materially  modified  by  Helm- 
holtz.  It  seems  to  offer  the  most  plausible  explanation  and 
is  the  one  probably  most  generally  accepted.  The  other 
theory  is  that  of  Ewald  Hering,  which  explains  colors  upon 


THE    EYE   AND   THE    PHYSIOLOGY   OF   VISION.  569 

an.  entirely  different  basis.  Both  theories,  however,  start 
from  facts  and  observations  which  are  afforded  by  instances 
of  color  blindness,  and  so  before  giving  these  theories  it 
may  be  desirable  to  describe  somewhat  in  detail  the  various 
kinds  of  color  blindness  observed.  Two  distinct  kinds  of 
color  blindness  are  found  called  respectively  monochro- 
matic, and  dichromatic  colorblindness.  Of  the  dichromatic 
blindness  two  varieties  occur  called  red  blindness  and  green 
blindness.  More  correctly,  however,  the  terms  monochro- 
matics  and  dichromatics  are  applied  to  the  persons  them- 
selves showing  these  defects. 

COLOE  BLINDNESS. 

Monochromatics .  As  the  name  indicates,  these  are  per- 
sons who  see  but  one  color.  This  color  seems  to  be  a  bluish 
white.  Such  monochromatics  see  the  world,  about  as  we 
do,  as  far  as  distinctness  is  concerned.  They  can  recognize 
objects  readily.  The  world  appears  to  them  about  as  it 
appears  to  us  in  a  photograph  or  an  etching.  It  will  be 
remembered  that  in  photographs  and  etchings  but  shades 
of  white  and  dark,  as  a  rule,  are  used.  Yet  so  true  may  a 
photograph  be,  using  only  these  two  colors,  that  we  fail  to 
notice  frequently  the  absence  of  the  spectral  tints.  It  is 
even  possible  for  such  monochromatics  to  live  for  some 
time  without  really  suspecting  their  defect,  attributing  their 
lack  of  color  perception  frequently  to  stupidity  in  that  di- 
rection rather  than  a  real  optical  disability.  Such  mono- 
chromatics  show  when  they  are  looking  at  objects  a  pecu- 
liar habit  of  squinting  the  eye,  as  if  they  were  focussing 
with  effort.  They  seem  to  have  some  difficulty  to  turn 
their  point  of  acutest  vision  on  the  object  in  question. 
Strange  as  it  may  seem,  such  monochromatics  may  some- 
times successfully  recognize  colors,  but  when  they  do  so  it 
is  for  the  same  reason  that  a  photographer  may  recognize 
colors  on  his  photograph,  having  learned  by  experience 
what  the  appearance  of  red  or  yellow  in  the  photograph  will 
be,  and  so  these  monochromatics  having  red  pointed  out 


570  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

to  them  repeatedly  they  are  sometimes  enabled  to  recognize 
Ihe  red  by  a  slightly  different  appearance  which  it  shows  to 
them  in  their  single  color. 

Monochromatic  color-blindness  is  not  very  general.  Rel- 
atively few  cases  have  been  scientifically  noted.  The  ex- 
planation of  the  phenomena  of  monochromatic  eyes  will  be 
explained  in  terms  of  each  theory  further  on. 

Dichromatics .  Dichromatic  eyes  see  but  two  colors. 
These  are  blue  and  yellow.  Of  course  black  is  not  counted 
as  a  color  in  any  of  the  eyes,  black  being  simply  the  absence 
of  light,  and  in  this  sense  it  would  be  correct  to  say  that  a 
totally  blind  individual  could  still  see  black.  These  dichro- 
matic eyes  see  the  blue  about  as  we  do,  but  instead  of  green, 
yellow  and  red,  they  see  but  yellow  alone. 

1. — Green- Blindness.  Two  distinct  varieties  of  dichro- 
matic eyes  occur.  The  varieties  are  so  marked  off,  that 
gradations  from  one  into  the  other  do  not  seem  to  exist. 
One  variety  of  dichromatic  eyes  sees  yellow  where  we  see 
red,  but  sees  no  definite  tint  where  we  see  green.  Such  per- 
sons are  called  green-blind.  They  seem  to  their  friends  to 
be  perfectly  able  to  recognize  the  red,  but  the  red  is  to  them 
really  an  intense  yellow,  which  they  have  learned  to  call  red 
because  it  has  always  been  pointed  out  to  them  as  red, 
while  green  they  are  not  able  to  recognize  except  as  a  paler 
yellow,  and  this  inability  to  readily  pick  out  green  objects 
has  given  them  the  name  of  green-blind  persons. 

2. — Red- Blindness.  In  the  second  variety  of  dichro- 
matic eyes  (a  variety  which  is  more  numerous  than  either 
of  the  others)  the  yellow  is  seen  most  intense  where  we  see 
green,  while  our  red  is  to  them  a  very  indistinct  color  some- 
thing like  a  pale  yellow.  They  readily  pick  out  green  ob- 
jects, because  these  appear  to  them  a  bright  yellow,  calling 
them  green,  however,  for  reasons  explained  above.  Such 
persons  not  being  able  to  clearly  distinguish  the  red  are 
called  red-blind  persons. 


THE    EYE    AND    THE    PHYSIOLOGY    OF   VISION.  571 

It  is  said  that  about  one  female  in  twenty-five  is  affected 
with  color  blindness  of  one  variety  or  another,  and  about 
one  male  in  every  eight  or  ten.  Red-blindness  is  the  more 
frequent  defect.  It  is  hard  to  explain  the  relatively  higher 
per  cent,  of  color-blindness  in  men,  unless  it  is  due  to  the 
fact  that  they  pay  relatively  less  attention  to  colors  and  that 
this  neglect  in  their  visual  education  has  contributed  to  this 
defect. 

What  we  call  green-blindness  and  red-blindness  are,  after 
all,  varieties  of  the  same  defect,  for  red-blind  and  green- 
blind  alike  see  blue  and  yellow  only.  In  the  green-blind 
people  our  red  seems  a  most  intense  yellow,  while  in  red- 
blind  people  our  green  seems  most  intense.  As  it  is  ex- 
ceedingly necessary  in  many  professions,  especially  that  of 
navigation  and  railroading,  that  employes  shall  be  able  to 
readily  distinguish  between  a  green  signal  and  a  red  danger 
signal,  such  corporations  now  very  generally  subject  their 
employes  to  a  very  careful  color  test  in  order  to  preclude 
as  much  as  possible  an  accident  from  such  a  lack  of  dis- 
crimination. 

With  a  general  description  of  these  three  varieties  of 
color-blindness  we  are  enabled  to  understand  possibly  a 
little  more  readily  each  of  the  two  attempts  made  to  explain 
them,  as  well  as  the  color  sensations  of  the  normal  eye. 

THE  YOUNG-HELMHOLTZ  THEORY. 

According  to  this  theory  there  are  found  in  the  retina 
three  kinds  of  nerve  fibers,  physiologically  considered.  To 
these  three  different  kinds  of  fibers  are  attributed  respect- 
ively sensations  of  red,  green  and  blue.  The  sensation  of 
blue  is  attributed  to  the  rods.  It  will  be  remembered  that 
the  rods  are  scattered  over  the  entire  retina  but  are  wanting 
in  the  yellow  spot,  for  which  reason,  if  this  theory  be  true, 
the  yellow  spot  should  be  blind  to  sensations  of  blue.  And 
such  seems  really  to  be  the  case.  If  with  proper  apparatus 
one  arranges  a  blue  point  in  such  a  way  that  it  shall  fall 
right  in  the  fovea  centralis,  it  seems  to  disappear,  while  red 


572  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

and  green  points  persist.  In  the  author's  own  experience 
such  a  disappearance  of  the  blue  when  falling  right  in  the 
fovea  centralis  seems  unquestionable  from  repeated  experi- 
ments. There  is,  however,  a  cause  that  might  produce  the 
disappearance  of  the  blue  point  apart  from  the  absence  of 
the  cones.  It  will  be  remembered  that  the  fovea  centralis 
lies  in  the  yellow  spot,  and  we  know  that  yellow  light  very 
rapidly  absorbs  blue  light.  Blue  light  does  not  readily  pass 
through  a  yellow  window  pane,  and  so  the  disappearance  of 
a  blue  point  on  the  retina  may  be  due  to  the  fact  that  the 
yellow  pigment  of  the  yellow  spot  absorbs  the  blue  light  and 
so  prevents  it  from  affecting  the  retina. 

According  to  the  Helmholtz  theory,  however,  the  blind- 
ness of  the  yellow  spot  with  reference  to  blue  is  due  to  the 
absence  of  the  rods.  The  rods  being  distributed  over  all 
other  portions  of  the  retina  explains  why  blue  is  thus  gen- 
erally present.  It  will  also  be  remembered  that  the  vision 
purple  found  in  the  eye  occurs  only  in  the  rods,  and  so  this 
theory  goes  a  point  further  suggesting  that  it  is  a  chemical 
action  of  the  vision  purple  produced  by  the  light  that  irri- 
tates the  rods  and  so  occasions  a  nervous  impulse  leading 
to  the  perception  of  blue. 

Monochromatic  eyes  are  upon  this  theory  explained  as 
eyes  in  which  the  rods  alone  are  functional.  The  yellow 
spot  is  then  entirely  blind,  and  to  this  blindness  of  the  yel- 
low spot  is  attributed  the  difficulty  in  focussing  and  the 
habitual  squinting  which  marks  monochromatic  persons. 
The  points  of  acute  vision  in  these  monochromatics  not  be- 
ing a  definite  spot,  but  a  circle  around  that  spot,  the  at- 
tempt to  keep  the  focus  on  this  circle  occasions  their  extra 
efforts  in  looking  closely. 

But  even  normal  eyes  are  monochromatic  at  times. 
When  the  ordinary  light  of  day  is  very  much  reduced,  as  it 
is  some  time  after  sunset,  we  notice  how  the  sensation  red 
disappears  first,  then  green,  while  blue  is  the  last  sensation 
to  go.  Every  one  must  have  noticed  that  a  night  scene  has 
a  bluish  cast.  Pictures  of  night  scenes  are  purposely  tinted 


THE   EYE   AND  THE   PHYSIOLOGY  OF  VISION.  573 

blue.  A  moonlight  scene  in  a  picture  is  readily  distin- 
guished from  a  view  by  day  in  the  absence  of  all  reds,  and 
the  prevailing  tint  of  blue.  In  subdued  light  red  and  green 
disappear,  and  things  before  they  shade  into  blackness 
seem  to  pass  through  gradations  of  deeper  and  deeper  blue. 
According  to  this  theory  we  have  lost  the  use  of  the  cones 
and  our  vision  is  limited  to  the  rods.  Therefore,  we,  too, 
ought  to  be  blind  in  the  yellow  spot,  as  this  possesses  no 
rods,  and  the  holders  of  this  theory  in  support  of  this,  point 
out  the  difficulty  we  have  in  distinct  vision  even  when  the 
light  would  still  be  strong  enough  to  permit  the  details  to 
be  seen  carefully. 

Dichromatic  eyes  are  explained  by  supposing  that  in  ad- 
dition to  the  rods  which  see  blue,  there  are  cones  which 
see  yellow,  and  the  two  varieties  of  dichromatic  eyes  are 
explained  by  the  relative  ease  with  which  these  yellow 
cones  are  stimulated.  In  red-blind  individuals  they  are 
stimulated  most  readily  by  green  objects;  in  green-blind 
persons  the  yellow  cones  are  stimulated  most  readily  by 
red  objects. 

NORMAL  OR  TRICHROMATIC  EYES. 

In  the  normal  eye  this  theory  supposes,  as  was  stated, 
three  sensations:  blue,  green  and  red.  A  grievous  fault  of 
this  theory  is  its  inability  to  explain  why  the  second  color 
in  dichromatic  eyes  should  be  yellow,  and  why  this  color 
should  not  be  represented  at  all  in  the  trichromatic  eyes. 
One  would  naturally  suspect  that  in  normal  eyes  the  ad- 
dition would  be  made  to  the  blue  and  yellow  of  partially 
color-blind  eyes.  It  was,  in  fact,  this  difficulty  to  explain 
how  the  yellow  of  dichromatic  eyes  was  replaced  by  green 
and  red  of  the  trichromatic  eyes  that  led  to  the  proposal  of 
the  Hering  theory,  which  explains  this  point  at  least  satis- 
factorily. 

It  will  be  noticed  that  a  normal  eye  might  be  derived 
from  the  composition  of  a  green-blind  eye  and  a  red-blind 
eye.  Thus  dichromatics  see  blue  just  as  we  do.  This  is 


574 


STUDIES    IN    ADVANCED    PHYSIOLOGY. 


one  color.  The  green-blind  people  see  our  red,  although  it 
is  yellow  to  them.  In  other  words,  their  sense  of  sight  is 
aroused  by  what  we  call  red.  This  is  the  second  color. 


Fig.  179.— DIAGRAMMATIC  REPRESENTATION  OF  THE  STRENGTHS  OF  THE  THREE  FUNDA- 

"  MENTAL  SENSATIONS  IN  THE  DIFFERENT  PARTS  OF  THE  SPECTRUM. 

J,  curve  for  color  red;  #,  curve  for  green;  3,  curve  for  blue.  The  red  curve  should 
show  a  small  added  elevation  at  the  violet  end,  since  the  stronger  reappearance  of  the 
red  there  causes  with  the  blue  the  production  of  the  violet. 

In  red-blind  persons  the  sensation  of  yellow  is  produced  by 
what  we  call  green.  Such  a  composition  of  two  dichro- 
matic eyes  would  therefore  be  (1)  blue,  (2)  yellow  where 
we  see  green,  (3)  and  yellow  where  we  see  red.  Now,  it 
is  just  possible  that  for  psychological  reasons  this  primitive 
yellow  sensation  has  been  divided  into  two  separate  sensa- 
tions which  we  have  learned  to  call  red  and  green.  One 
can  easily  understand  how  by  having  two  colors,  even  if 
they  are  somewhat  alike,  side  by  side  before  the  eye,,  that 
it  would  tend  to  make  distinctions  which  would  otherwise 
go  unnoticed. 

The  normal  eye  is  usually  spoken  of  as  a  trichromatic 
eye  because  of  its  ability  to  perceive  three,  different  sensa- 
tions. By  the  varying  compositions  of  these  different  sen- 
sations all  the  shades  and  tints,  and  intermediate  colors 
may  easily  be  derived.  When  all  three  fibers  in  the  eye 
are  stimulated  in  the  proper  proportion,  white  is  the  result. 
This  may  be  shown  to  be  true  by  taking  a  card  on  which 
the  red,  green  and  blue  are  put  in  the  proper  proportion 
and  then  whirling  it  rapidly.  The  three  colors  melt  to- 
gether and  the  sensation  of  white  results.  The  red  and  the 


THE   EYE   AND   THE   PHYSIOLOGY   OF   VISION.  575 

blue  produce  purple.  Red  and  white  a  sensation  in  which 
the  red  nerves  are  more  stimulated  than  in  the  proportion 
of  white,  produces  pink.  Violet,  although  usually  indi- 
cated in  elementary  books  as  one  of  the  fundamental  color 
sensations,  is  in  reality  not  one,  but  is  a  mixture  of  the  blue 
and  red,  for  it  will  be  remembered  when  the  number  of 
vibrations  of  the  various  colors  was  given  that  it  was  pointed 
out  that  the  violet  was  just  an  octave  above  the  red,  and 
that  the  red  seemed  to  appear  again  there  mixed  with  the 
blue.  It  was  pointed  out  in  the  case  of  sound  that  a  string 
set  in  vibration  by  a  certain  sound  would  be  readily  affected 
by  its  octave.  So  a  nerve  in  the  retina  that  is  affected  by 
red  seems  also  affected  by  an  octave  of  red,  and  for  that 
reason  blue  will  gradually  "shade  into  the  violet  as  the 
octave  of  the  red  is  there  approached.  As  the  sensation  of 
blue  was  attributed  to  the  rods,  yellow  and  green  sensa- 
tions and  the  colors  into  which  they  enter  are  attributed  to 
the  cones. 


R  0          Y          Gr  Bl  V 

Fig.  180. — GRAPHIC  REPRESENTATION  OF  THE  COMPOSITION  OF  COLOR  SENSATIONS  IN 

TERMS    OF    THK    YOUNG-HELMHOLTZ    THEORY.     THE    CURVES    FOR    RED.   GREEN  AND 
BLUE   ARE   HERE   SUPERIMPOSED. 

THE  BERING  THEORY. 

According  to  the  theory  of  Hering  there  are  in  the  retina 
three  different  color  substances  which  are  either  in  process 
of  being  made,  assimilation,  or  in  process  of  destruction, 
dissimilation.  One  of  these  color  substances  he  calls  his 
white-black  substance.  When  this  substance  is  being  pro- 
duced in  the  eye  the  sensation  of  black  results;  when  it  is 
being  destroyed  in  the  eye  the  sensation  of  white  results. 
Hence,  objects  appear  white  when  the  light  falling  into 
the  eye  causes  this  white-black  substance  to  disintegrate. 
Things  appear  black  when  on  that  point  of  the  retina  this 
white-black  substance  is  being  formed. 


576  STUDIES    IN   ADVANCED    PHYSIOLOGY. 

Hering  explains  monochromatic  eyes  as  eyes  that  pos- 
sess but  this  white-black  substance.  He  questions  the 
bluish  tint  which  many  monochromatics  have  and  explains 
the  appearance  of  the  world  as  monochromatics  see  it  as 
that  of  a  black  and  white  steel  engraving.  As  this  white- 
black  substance  is  produced  when  no  light  enters  the  eye 
things  seem  black  in  the  absence  of  light. 

Dichromatics  possess  in  addition  to  this  white-black 
substance  a  blue-yellow  substance.  This  substance  when 
it  is  being  destroyed  in  the  eye  produces  blue ;  when  it  is 
being  re-formed  in  the  eye  produces  yellow  sensations. 
Looking  at  a  blue  object  according  to  this  theory  would 
produce  a  disintegration  of  this  substance,  which  would 
occasion  the  sensation  blue,  while  looking  at  a  yellow  ob- 
ject would  cause  the  production  of  some  of  this  substance 
and  in  this  way  the  retina  be  affected  to  see  yellow. 

Finally,  in  normal  eyes  there  is,  in  addition  to  the 
white-black  substance  and  the  blue-yellow  substance,  a  red- 
green  substance.  Here,  too,  a  disintegration  of  the  same 
produces  red,  a  production  of  it,  green  sensations.  While 
this  theory  seems  very  fanciful  at  first,  it  explains  the 
dichromatic  eyes  and  further  gives  us  a  reason  for  many  of 
the  phenomena  which  may  be  observed  in  studying  after- 
images and  color  contrasts. 

AFTER-IMAGES. 

An  after-image  is,  as  the  name  suggests,  an  image  re- 
tained on  the  retina  after  the  stimulus  producing  it  has 
ended.  Such  after-images  may  be  of  two  kinds:  positive, 
when  they  have  the  same  color  as  the  object,  or  negative, 
when  they  have  the  complementary  color. 

1. — Positive  After- Images.  The  forming  and  dis- 
appearance of  an  image  on  the  retina  is,  from  a  physical 
standpoint,  as  instantaneous  as  the  changes  of  light,  but 
the  sensation  which  this  image  produces  will  sometimes 
continue  after  the  stimulus  is  gone.  Thus,  a  sky  rocket 
seems  to  leave  a  trail  of  fire  after  it ;  a  red-hot  coal  swung 


THE    EYE    AND   THE    PHYSIOLOGY   OF   VISION.  577 

around  on  a  string  looks  like  a  luminous  circle ;  a  point  of 
light  moving  rapidly  up  and  down  looks  like  a  luminous 
stick.  All  this  is  explained  on  the  ground  that  the  sensa- 
tions linger  and  that  we  therefore  see  the  rocket  in  a  cer- 
tain position  after  it  has  left  it  and  attained  a  new  one. 
We  see  a  rapidly  moving  luminous  object  in  the  position  in 
which  it  is  at  the  moment,  together  with  quite  a  number 
of  positions  through  which  it  has  just  passed,  and  in  that 
way  its  path  becomes  luminous.  A  rapidly  rotating  wheel 
shows  none  of  the  spokes  distinctly  for  similar  reasons. 
If,  in  a  room  lighted  by  a  gas  jet,  the  gas  be  suddenly 
turned  off  while  one  is  looking  at  it,  an  image  of  the  flame 
remains  an  instant  or  two  after  that  on  the  retina.  Pos- 
sibly the  most  familiar  illustration  of  this  fact  is  in  the 
lightning,  a  stroke  of  which  seems  to  us  to  extend  in  a 
continuous  although  zig-zag  line  from  the  cloud  to  the 
earth. 

Positive  after-images  retain  not  only  the  shape,  but  also 
the  color  of  the  object  and  offer  no  serious  difficulty  in  their 
explanation.  It  is  not  so  easy  with  negative  after-images. 

2. — Negative  After- Images.  If  one  glances  at  the  sun 
just  an  instant  and  then  looks  up  into  the  sky  in  a  differ- 
ent direction  one  sees  a  round  black  disk.  If  one  looks  in- 
tently with  the  eyes  fixed  on  a  red  light  and  then  shifts 
his  view  to  a  white  wall  an  image  of  the  light  looked  at  is 
projected  against  the  wall  but  in  different  colors,  usually 
bluish  or  greenish.  Or,  if  one  looks  out  of  the  window 
intently  for  some  time,  then  turns  the  look  to  the  wall, 
the  white  window  panes  are  black,  the  black  window 
frames  somewhat  light  in  the  negative  after-image.  An 
after-image  retains  the  form  and  size  of  the  real  image,  but 
in  its  complementary  colors.  A  very  clear  illustration  of 
this  on  a  wider  scale  is  afforded  by  placing  close  before  the 
eye  an  intensely  red  light  and  looking  at  the  same  for  some 
time,  even  at  the  risk  of  tiring  the  eye.  Upon  turning  now 
to  a  room  lighted  with  electricity  or  gas  light,  or  even  ordi- 
nary day  light,  the  objects  possess  an  intensely  bluish  tint, 
37 


578  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

which  only  gradually  fades  and  disappears.  Here  the  entire 
retina  having  been  stimulated  with  red,  everything  later  pic- 
tured upon  it  is  clothed  with  bluish  tints  the  complementary 
color  of  red.  We  have  now  to  consider  how  these  negative 
after-images  are  accounted  for  by  Young's  theory  and  by 
Hering's. 

EXPLANATION  OF  NEGATIVE  AFTER-IMAGES. 

These  negative  after-images  are  explained  by  the  Young- 
Helmholtz  theory  as  due  to  the  fatigue  of  the  retina.  If 
one  looks  intently  for  some  time  at  a  red  light  evidently  the 
red  nerves  of  that  part  of  the  retina  on  which  this  image 
falls  will  be  stimulated,  while  the  green  and  the  blue  nerves 
are  resting.  If  this  stimulation  continues  it  is  evident  that 
these  red  nerves  will  become  fatigued.  There  will  be  a 
tendency  for  the  red  object  to  become  paler  and  paler  as  this 
effect  proceeds.  If,  now,  the  eye  be  turned  upon  a  white 
wall  the  entire  retina  is  flooded  with  white  light.  In  that 
part  of  the  retina  where  the  red  image  was  the  red  nerves  are 
fatigued  and  so  do  not  respond;  at  least  not  fully.  The  con- 
sequence is  that  the  green  and  blue  nerves  react  alone  and 
so  that  area  appears  a  greenish-blue  or  a  bluish-green.  As 
the  red  nerves  gradually  recover  from  their  fatigue  their 
stimulation  is  mixed  with  the  blue  and  green,  which  of 
course  produces  white.  This  explains  very  satisfactorily  the 
complementary  color  of  the  negative  after-image  and  how  it 
is  gradually  transformed  back  into  white. 

But  not  only  may  one  nerve  be  thus  fatigued;  two  or 
even  three  may  be  so  affected.  If  one,  for  instance,  gazes 
at  the  sun  an  instant  the  image  of  the  sun  falling  on  the 
retina  and  strongly  stimulating  that  portion,  fatigues  it. 
When,  now,  the  view  is  turned  in  another  direction  this  por- 
tion of  the  retina  which  the  sun's  image  had  fatigued  fails 
to  be  fully  excited,  and  so  there  arises  the  sensation  of 
black,  or,  if  the  excitation  is  only  a  partial  one,  shades  of 
gray. 


THE   EYE   AND   THE    PHYSIOLOGY   OF   VISION.  579 

This  theory  also  explains  why  looking  from  one  color  to 
a  complementary  one  seems  to  increase  the  brightness  of 
the  second.  An  animal  grazing  in  the  field  and  seeing  prac- 
tically nothing  all  day  except  the  green  grass  and  the  green 
foliage,  has  a  much  more  vivid  impression  of  a  red  object 
when  this  is  suddenly  presented,  than  it  would  otherwise 
have,  the  explanation  being  that  the  red  nerves  have  been 
resting  all  day,  and  then  suddenly  stimulated  they  react 
with  great  energy.  The  offense  which  certain  animals  seem 
to  take  at  such  bright  objects  flared  at  them  may  be  to  a 
slight  extent  at  least  accounted  for  in  this  way.  Every 
stroller  through  the  woods  must  have  been  struck  with  the 
intense  redness  of  a  summer  redbird  or  a  cardinal  as  it 
darted  in  among  the  green  leaves. 

In  terms  of  the  Hering  theory  negative  after-images  are 
explained  as  follows: 

Taking,  for  instance,  the  supposed  red-green  substance 
of  the  eye  which  when  it  is  being  destroyed  produces  red 
sensations,  when  it  is  being  regenerated  produces  green,  it 
seems  entirely  possible  that  the  excessive  destruction  of  it 
might  induce  its  regeneration.  Just  like  an  active  destruc- 
tion of  muscle  tissue  is  the  occasion  for  a  corresponding 
active  regeneration  of  it.  An  increased  use  of  any  product 
of  the  body  very  naturally  brings  about  an  increased  pro- 
duction. 

Turning  now  to  the  first  illustration,  it  is  supposed  that 
while  the  eye  is  looking  intently  at  a  red  object  this  red- 
green  substance  is  in  that  part  of  the  retina  where  the  image 
falls  being  used  up,  and  if  the  look  continues,  is  being  ex- 
hausted rapidly.  If,  now,  the  eye  is  turned  away  there  is 
naturally  induced  an  attempt  of  the  eye  to  produce  some 
new  substance  of  this  kind,  and  this  regeneration  acting  as 
a  stimulus  gives  us  the  sensation  of  green.  So  with  the 
other  two  substances.  If  the  white-black  substance  had  at 
some  point  of  the  retina  been  almost  exhausted  by  staring 
an  instant  at  the  sun,  say,  there  would  occur  at  that  point 
in  the  retina  as  soon  as  the  eye  was  turned  away  a  regener- 


580  STUDIES   IN    ADVANCED    PHYSIOLOGY. 

ation  of  this  substance,  and  so  a  sensation  of  black.  It  is 
unnecessary  to  carry  this  further  with  the  yellow-blue  sub- 
stance. 

If  two  substances  were  simultaneously  being  exhausted 
then  there  would  be  induced  the  regeneration  of  both,  and 
in  this  way  there  would  arise  in  the  eye  various  intermedi- 
ate colors  corresponding  to  the  intermediate  colors  first 
looked  at.  It  is  apparent  that  the  negative  after-image 
will  be  not  far  from  the  complementary  color  of  the  object 
looked  at. 

It  will  thus  be  seen  that  both  theories  account  more  or 
less  satisfactorily  for  many  of  the  phenomena  of  color  sen- 
sation, and  each  reader  will  have  to  decide  for  himself  the 
relative  probability  of  these  two  views.  A  point,  very  much 
in  favor  apparently  of  the  Young-Helmholtz  theory  lies  in 
the  fact  that  owls  and  bats,  which  from  their  habits  would 
naturally  be  suspected  of  being  monochromatics,  possess 
rods  only,  the  cones  being  entirely  absent.  A  second 
point  in  its  favor  is  the  observation  that  we  are  not  able  to 
see  red  towards  the  periphery  of  the  retina.  For  instance, 
if  one  take  a  red  object,  such  as  a  stick  of  red  sealing-wax, 
and  move  it  from  behind  the  head  forwards  it  does  not  ap- 
pear red  at  first,  and  must  be  moved  some  distance  .further 
even  after  its  outline  is  recognizable,  when  suddenly  the 
sensation  red  flashes  into  consciousness.  Blue  and  green, 
however,  are  more  readily  recognized  at  the  periphery. 
Now,  in  terms  of  the  Hering  theory  it  would  be  impossible 
to  see  green  where  one  cannot  see  red,  since  one  substance 
is  the  cause  of  both.  The  explanation  that  suggests  itself 
is  that  green  and  blue  nerves  occur  here  only,  the  red 
ones  being  absent. 

DOUBLE   VISION. 

So  far  everything  that  has  been  said  would  apply  if  we 
had  but  one  eye,  but,  as  a  matter  of  fact,  we  use  two  eyes 
in  looking  at  objects  and  the  question  naturally  arises,  why 
vision  with  two  eyes  should  result  in  an  apparently  simple 


THE    EYE    AND    THE    PHYSIOLOGY    OF    VISION.  581 

visual  sensation.  Every  normal  individual  when  looking 
directly  at  an  object  sees  It  as  one  object.  It  is  possible, 
however,  to  see  objects  double,  of  the  truth  of  which  one 
may  easily  satisfy  himself  by  holding  a  pencil  before  his 
eyes  and  then  looking  past  the  pencil  into  the  distance. 
He  will  perceive  two  pencils.  Of  course  if  he  turns  his 
focus  upon  the  pencil  before  him  the  two  pencils  will  melt 
into  one  and  the  object  appear  single.  But  in  that  case 
the  objects  in  the  distance  appear  more  or  less  double. 
There  are  on  the  retinas  corresponding  points,  the  simul- 
taneous stimulation  of  which  produces  in  the  mind  but  a 
^single  sensation,  and  we  ordinarily  see  objects  single  be- 
cause we  turn  to  the  object,  corresponding  points.  If,  on 
the  other  hand,  the  image  of  anything  should  fall  on  points 
which  do  not  correspond,  each  image  will  produce  its  own 
sensation  and  so  we  see  double. 

To  determine  which  are  corresponding  points  of  the  ret- 
ina it  is  only  necessary  to  imagine  the  retina  of  one  eye 
laid  right  over  the  retina  of  the  other  eye  in  such  a  way 
that  the  yellow  spots  would  coincide  as  well  as  the  merid- 
ians passing  through  the  yellow  spots.  In  that  case  the 
points  lying  immediately  above  and  below  each  other  are 
corresponding  points.  For  a  point  in  the  upper  and  outer 
part  of  the  retina  of  the  right  eye,  the  corresponding  point 
of  the  left  eye  would  be  found  in  the  upper  inner  portion. 
Reference  to  Figures  181  and  182  will  help  to  clarify  this. 
Thus,  in  Figure  181  the  gaze  is  directed  for  the  point/", 
which  is  seen  as  a  single  point  because  its  images  at  c  and 
c  fall  on  corresponding  points,  but  the  point  g  is  seen 
double  at  G  and  G2  because  the  images  of  it  fall  on  points 
g  and  g2  which  do  not  correspond.  The  corresponding 
point  to  g  is  of  course  g'A .  Turning  now  to  the  next  fig- 
ure in  which  the  point  G  is  seen  single  because  its  images 
at  c  and  c  fall  on  corresponding  points,  f  is  seen  double  at 
F'  and  F~ ,  because  the  images  of  point  f  fall  at  f  and/"', 
which  are  not  corresponding  points,  the  corresponding 
point  to  f  being/"3. 


582  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

From  these  figures  it  will  be  seen  that  only  one  point 
can  be  seen  single  at    one    time;    all    other    points   appear 


C9,  92"  " .  T3 

Fig.  181.  Fig.  182. 

Figs.  181  and  182.— DIAGRAMS  TO  SHOW  THE  ORIGIN  OF  DOUBLE  VISION. 

more  or  less  distinctly  double.  We  are  not  aware  of  the 
doubleness  of  these  outside-lying  points  for  the  following 
reasons: 

First.  To  see  an  object  clearly  we  turn  to  it  the  yellow 
spots  of  both  eyes,  which  are  corresponding  points.  Hence 
all  objects  seen  distinctly,  that  is,  with  the  yellow  spot, 
appear  single. 

Second.  The  other  portions  of  the  retina  are  not  so  sen- 
sitive as  the  yellow  spot,  and  so  the  doubleness  of  the 
image  does  not  press  itself  into  the  field  of  consciousness. 

Third .  Attention  is  usually  riveted  to  those  objects  only 
which  fall  in  or  very  close  to  the  yellow  spot,  and  we  do 
not  take  cognizance  of  objects  falling  on  the  periphery  of 


THE    EYE    AND    THE    PHYSIOLOGY    OF   VISION. 


583 


the  retina.  A  somewhat  curious  exception  to  this  rule  of 
double  vision  is  found  in  viewing  the  starry  heavens.  Here 
all  the  stars  appear  as  single  stars,  whether  the  image  falls 
close  to  the  yellow  spot  or  on  the  periphery.  This  arises 
from  the  fact  that  owing  to  the  immense  distances  of  these 
objects  the  rays  coming  from  them  are  practically  parallel, 
and  entering  the  eye  in  parallel  lines  all  the  images  must 
naturally  fall  upon  corresponding  points.  Reference  to 
Figure  183,  in  which  the  rays  of  light  from  one  star  are 
given  as  lines  1  and  7,  and  rays  from  the  second  star  given 
as  lines  2  and  2,  it  will  be  seen  that  c  and  c  and  a  and  a 
are  corresponding  points. 


c  *  c, 

Fig.  183  —DIAGRAM  SHOWING  THE  COMPLETE  CORRESPONDENCE  OF  RETINAL  POINTS  IN 

LOOKING  AT  VERY  DISTANT  OBJECTS,  SUCH  AS  STARS. 

THE  ADVANTAGES  OF  TWO  EYES. 

Even  if  one  eye  were  able  to  see  all  colors  as  perfectly 
as  two,  one  or  two  decided  advantages  arise  from  the  pos- 
session of  two  eyes. 

First.  The  defect  in  the  retina  caused  by  the  blind  spot 
is  remedied  by  the  opposite  eye,  as  the  corresponding  points 


584  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

for  the  blind  spot  of  one  eye  are  very  sensitive  points  of  the 
other.  In  a  similar  way  smaller  pathological  defects  in  the 
retina  of  one  eye  are  more  or  less  fully  counteracted  by  the 
other. 

Second.  We  are  enabled  to  look  at  the  same  object  from 
two  different  points  of  view,  and  so  can  see  more  of  the  ob- 
ject than  with  one  eye  alone.  This  vision  from  two  differ- 
ent points  gives  rise  to  the  perception  of  solidity.  One  may 
easily  satisfy  himself  that  notions  of  the  solidity  of  objects 
are  very  materially  dependent  upon  one's  seeing  them  with 
both  eyes.  The  stereoscope  is  based  upon  this  principle. 
Two  views  are  taken  of  the  same  scene  from  points  some 
distance  apart.  These  two  figures  are  then  mounted  in 
such  a  way  that  one  eye  sees  one  photograph,  the  other  eye 
the  photograph  from  the  other  corresponding  position.  In 
this  way  there  arises  the  sensation  of  solidity  to  such  an  ex- 
tent that  we  actually  seem  to  see  certain  portions  of  the  pic- 
ture projecting  in  front  of  the  others.  Of  course  the  two 
views  taken  must  not  be  from  remotely  removed  points.  In 
that  case  the  mind  is  unable  to  blend  the  two  pictures  into 
one,  and  recognizes  them  as  two  distinct  pictures. 

When  two  entirely  distinct  scenes  or  objects  are  brought 
one  to  one  eye  and  one  to  the  other,  the  two  eyes  seem  to 
strive  for  the  mastery,  and  sometimes  we  see  one  picture, 
then  suddenly  the  other.  This  contest  of  the  two  pictures 
is  not  really  a  process  of  the  eye ;  possibly  each  eye  sends 
the  image  of  the  picture  before  it  to  the  brain,  but  the  brain, 
unable  to  look  at  two  different  things  at  the  same  time, 
takes  cognizance  of  one,  then  of  the  other,  and  so  on. 
Such  a  result  naturally  occurs  in  persons  who  are  cross- 
eyed. .  In  such  individuals  the  corresponding  points  of  the 
retina  are  placed  entirely  awry,  and  each  eye  produces  its 
own  picture.  Only  one  of  these  pictures  rises  into  full  con- 
sciousness, or,  as  we  say,  cross-eyed  persons  select  one  eye 
to  look  with.  This  frequently  remains  the  same.  Some- 
times the  attention  is  shifted  to  the  other  eye,  which  then 
becomes  the  seeing  one. 


THE    EYE    AND    THE    PHYSIOLOGY   OF   VISION.  585 

Third.  By  determining  the  amount  of  motion  neces- 
sary to  move  the  view  of  the  eyeballs  from  one  point  to  an- 
other we  make  inferences  as  to  the  distance  absolute  and 
relative  of  the  objects  seen.  If  an  individual  closes  one 
eye  and  then  with  his  arm  and  finger  extended  forward, 
moves  towards  the  wall  with  the  intention  of  halting  when 
his  finger  is,  say  just  an  inch  from  the  wall,  he  will  find 
himself  quite  unable  to  do  this  satisfactorily,  sometimes 
touching  the  wall  while  he  thinks  he  is  still  several  inches 
away,  at  other  times  suspecting  the  distance  from  his  finger 
tip  to  the  wall  to  be  about  an  inch,  when  it  is  five  or  six  times 
that  amount.  His  inability  to  form  correct  judgments  of  dis- 
tance in  this  case  arises  from  the  lack  of  using  both  eyes. 

OPTICAL  ILLUSIONS. 

It  has  been  pointed  out  that  the  eye  is  enabled  to  give 
us  sensations  of  color  only.  All  knowledge  of  form,  size, 
distance,  solidity,  etc.,  are  inferences  made  by  the  mind. 
One  would  naturally  suspect,  therefore,  that  these  infer- 
ences would  occasionally  prove  faulty  and  so  give  rise  to  il- 
lusions, a  deception  which  we  then  attribute  to  our  physical 
senses  instead  of  holding  our  own  minds  responsible  for 
them. 

Several  of  the  more  striking  forms  of  illusions  are  men- 
tioned here. 

1. — Irradiation.  A  light  area  on  a  dark  background 
seems  larger  than  a  black  area  on  a  black  background, 
even  when  these  areas  are  mathematically  alike.  A  hole 
through  an  object,  such  as  a  wall,  or  even  a  piece  of  card- 
board, seems  larger  than  the  solid  piece  that  entirely  fills 
the  hole.  A  person  in  light  attire  seems  larger  than  in  dark 
attire.  The  explanation  of  this  lies  in  the  lack  of  sharp 
focussing  in  the  eye.  When  the  focus  of  an  object  does  not 
fall  directly  on  the  retina,  but  the  rays  of  light  strike  the 
retina  before  meeting  at  a  point,  it  is  evident  that  a  larger 
area  of  the  retina  is  affected.  Turning  to  Figure  184  it  is 
readily  seen  that  the  image  of  the  point  a  is  a  correspond- 


586 


STUDIES    IN    ADVAXCKD    PHYSIOLOGY. 


ing  point  on  the  retina  ;/  n  at  c.     If  the  focussing  were  not 
distinct  and  the  rays  of  light  should  strike  the  retina  as  they 


Fig.  184. — DIAGRAM  TO  SHOW  THK  EFFECTS  OF   IMPERFECT  FOCUSSING  IN  PRODUCING 

THE  PHENOMENA  OF  IRRADIATION. 

At  either  m,  m,  or  I,  I,  there  is  a  circular  field  of  light  instead  of  a  point  as  at  »,  n. 

do  at  m  m  or  at  /  /,  a  much  larger  portion  of  the  retina  would 
be  covered.  The  image  instead  of  being  a  point  would  be 
a  disk.  This  disk  covering  a  larger  portion  of  the  retina 
than  it  would  do  if  it  were  exactly  focussed,  produces  a  sen- 
sation which  is  interpreted  as  much  larger  in  extent.  Thus, 
also,  a  black  area  in  a  light  background  would  seem  larger 
than  it  naturally  is,  because  now  the  black  area  would  not 
be  sharply  focussed,  would  spread  over  more  retina  and  give 
rise  to  a  sensation  of  larger  extent.  For  this  reason  a  per- 
son in  dark  attire  would  seem  larger  when  projected  against 
a  white  background  just  as  a  person  in  light  attire  seems 
larger  when  projected  against  the  usual  dark  background. 

2. — Parallelism.  While  we  are  usually  able  to  distin- 
guish with  considerable  accuracy  the  parallelism  of  two 
lines,  there  arises  a  deception  when  these  lines  are  crossed 
with  diagonal  lines,  as  indicated  in  Figure  185,  where  the 
long  lines  are  parallel,  but  seem  not  to  be. 

3. — Distance.  We  judge  distance  in  several  ways;  by 
the  size  which  the  object  appears  to  us  to  have  when  its 
actual  size  is  known ;  by  the  distinctness  with  which  we  see 
it,  and  by  the  number  of  objects  which  lie  between  us  and 
it.  Unbroken  distances  are  as  a  rule  entirely  under-judged. 
This  is  due  to  the  fact  that  distances  in  which  many  objects 
are  found  seem  longer  than  distances  in  which  no  objects 


THE    EYK    AND    THK    PHYSIOLOGY   OF   VISION. 


587 


occur.     For  this  reason  ten  miles  on  a  level  prairie  with  a 
clear  view  seem  much  shorter  than  when  the  intervening 


Fig.  185.— OPTICAL  ILLUSION.    THE  PARALLELISM  OF  THE  LONG  LINES  is  DESTROYED  BY 

THE  CROSS-LINES. 

space  is  filled  with  a  multitude  of  striking  objects.  So  in 
Figure  186  the  distance  from  a  to  b  seems  longer  than  the 
distance  from  b  to  c.  For  a  similar  reason  the  first  square 
in  Figure  187  seems  higher  and  narrower  than  the  second. 
In  Figure  188  the  distance  from  a  to  b  seems  greater  than 
the  distance  from  c  to  d. 


ViZ>  186.  Fig.  187. 

Fififs.  186  and  187-7-OPTiCAL  ILLUSIONS. 

4. — Size.  Primarily,  the  size  of  an  object  depends  upon 
the  size  of  its  image  in  the  eye,  but  we  have  learned  by  ex- 
perience that  the  size  of  this  image  will  depend  upon  the 
distance  of  the  object.  Therefore,  when  we  know  the  dis- 
tance we  infer  the  size.  It  is  the  opposite,  in  short,  of  the 
inference  of  distance.  When  we  are  ignorant  of  the  dis- 
tance we  are  unable  to  judge  size  closely,  our  inferences 
being  then  based  wholly  upon  the  clearness  with  which  it 


588  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

can  be  seen  and  a  comparison  with  objects  lying  near  it. 
These  inferences  are  frequently  deceptive.  A  mountain 
which  on  account  of  its  immense  size  stands  out  so  clearly 
seems  for  that  reason  to  be  very  close,  and  many  a  deceived 
tourist  has  walked  miles  to  find  that  his  mountain  remained 
about  as  far  away  as  ever.  A  person  unaccustomed  to  the 
sea  seems  helpless  in  judging  distance,  and  therefore  size, 
and  the  guesses  made  by  a  group  of  passengers  on  board  of 
an  ocean  steamer  as  to  the  distance  and  size  of  a  certain 
vessel  on  the  horizon  will  sometimes  vary  from  one  mile  to 
twenty-five  in  the  matter  of  distance,  and  from  a  small  fish- 
ing smack  to  an  ocean  steamer  in  size. 


Fig:.  188. — OPTICAL  ILLUSION  OF  LENGTH. 

A  rather  interesting  deception  occurs  in  connection  with 
the  moon.  The  moon  seems  larger  near  the  horizon  than 
near  its  zenith.  Very  frequently  the  comparison  is  made  as 
between  a  wagon  wheel  at  the  horizon  and  a  cheese-box  at 
the  zenith.  This  apparent  change  in  the  size  of  the  moon 
arises  for  two  reasons.  First,  we  imagine  the  moon  to  be 
farther  away  when  near  the  horizon  that  when  directly 
overhead.  The  globe  of  the  heavens  seems  to  us  in  fact, 
a  flattened  inverted  bowl.  The  moon,  however,  having  the 
same  size  at  the  horizon  but  being  judged  by  us  farther 
away,  we  think  it  larger.  It  is  like  the  boy  in  the  fable 
who  projected  a  spider  hanging  from  his  hat  rim  against 
the  distant  heavens,  and  imagined  it  therefore  a  spectre 
reaching  from  the  earth  to  the  skies.  The  spider  appeared 
no  larger  than  it  really  was,  but  under  the  belief  that  it 


THE    EYE    AND    THE    PHYSIOLOGY    OF   VISION.  589 

was  miles  away  it  seemed  to  reach  into  the  clouds.  A 
second  reason  for  the  increased  size  of  the  moon  lies  in  the 
comparison  which  we  make  of  the  size  of  the  same  with  the 
objects  in  its  range.  We  see  for  instance  the  moon  about 
twice  as  wide  as  a  certain  chimney,  the  dimensions  of  which 
we  know,  and  in  an  unconscious  way  we  make  calculations 
as  to  the  moon's  size.  When  the  moon  is  overhead  there 
are  no  intervening  objects  and  the  comparison  does  not 
occur. 

5. — Shine  or  Brilliancy.  It  was  pointed  out  in  the  dis- 
cussion of  the  reflection  of  light  that  a  perfectly  smooth 
surface  reflected  the  light  in  an  unbroken  way  and  would 
appear  even  to  a  single  eye  polished  or  shiny.  But  the 
sensation  of  the  shine  or  brilliancy  of  a  surface  is  very 
much  increased  when  we  look  at  it  with  both  eyes.  This 
seems  to  be  due  to  the  fact  that  the  same  amount  of  light 
is  not  reflected  into  both  eyes.  It  is  apparent  that  the 
reflection  from  a  shining  surface  is  not  the  same  for  differ- 
ent directions.  Especially  is  this  true  if  that  surface  should 
move  slightly  as,  for  instance,  a  surface  of  water.  This 
slight  disagreement  between  the  sensations  of  brightness 
in  the  two  eyes  is  interpreted  by  the  mind  as  increased 
shine  or  brilliancy.  It  is  possible  experimentally  to  take 
two  surfaces,  neither  of  which  when  seen  alone  appearing 
polished,  and,  placing  one  before  each  eye  and  then  illu- 
minating them  with  different  intensities,  to  produce  a  sen- 
sation of  shine  or  brilliancy.  The  mind  seems  to  combine 
the  non-agreement  of  intensity  of  light  reported  by  the  two 
eyes  into  a  new  sensation.  In  this  way  arises,  for  instance, 
the  brilliancy  of  reflected  moonbeams  from  a  rippling  sur- 
face of  water. 

6. — Entopic  Illusions.  These  are  illusions  which  arise 
from  a  cause  lying  within  the  eye  itself.  They  are: 

(a)  Musccz  volitantes.  These  are  commonly  called  the 
flying  motes,  and  appear  as  little  black  spots  which  we  pro- 
ject into  space.  These  black  spots  are  due  to  shadows  which 


590  STUDIES    IN    ADVANCED    PHYSIOLOGY. 

small  opaque  bodies  in  the  vitreous  humor  throw  against 
the  retina,  which  shadows  we  by  mistake  project  outside  of 
the  eye.  These  opaque  bodies  in  the  vitreous  humor  are 
remnants  of  embryonic  blood-vessels. 

(b)  The  figures  of  Piirkinje.  These  are  figures  pro- 
duced by  the  shadows  which  the  blood-vessels  of  the  retina 
throw  against  the  retina.  The  blood-vessels  lie  in  the  outer 
coats  of  the  retina,  and  so  whenever  light  enters  the  eye 
they  cast  a  shadow  on  the  deeper  sensitive  layers.  Ordi- 
narily we  do  not  notice  this  shadow  because  we  have  been 
accustomed  to  it,  as  the  shadows  always  fall  on  the  same 
points  of  the  retina,  the  light  entering  always  at  the  pupil. 
In  the  same  way  we  might  become  insensible  to  an  object 
resting  on  a  certain  portion  of  the  skin  if  it  should  remain 
there  for  any  great  length  of  time.  When,  however,  the 
object  is  suddenly  placed  on  a  new  bit  of  skin  it  produces  a 
distinct  sensation,  so  when  the  shadows  of  these  blood- 
vessels fall  on  a  new  part  of  the  retina  we  at  once  distinctly 
see  them,  and  as  usual  project  these  shadows  out  into  space. 
If  an  individual  go  into  a  room  lighted  only  with  a  lamp  and 
then  move  the  lamp  at  one  side  of  his  head  in  such  a  way 
that  the  light  of  the  lamp  pass  through  the  white  portion  of 
the  eye  on  that  side  instead  of  through  the  pupil,  he  will 
suddenly  see,  especially  if  he  look  against  a  white  wall,  a 
branched  system  of  vessels,  and  if  the  experiment  is  very 
successful  may  even  note  the  translation  of  the  individual 
corpuscles  through  these  blood-vessels.  The  explanation 
is  apparent.  The  light  entering  through  the  sclerotic  por- 
tion of  the  eye  causes  the  blood-vessels  to  cast  a  shadow  in 
a  different  direction  than  when  the  light  normally  enters 
the  pupil,  and  this  shadow  falling  upon  a  new  portion  pro- 
duces a  sensation.  These  Purkinje  figures  may  be  pro- 
duced upon  suddenly  emerging  into  the  light  after  having 
been  confined  for  some  time  in  a  dark  space,  or  after  a 
night's  sleep  upon  suddenly  opening  the  eyes.  In  this  case 
the  retina  where  the  shadow  normally  falls  has  been  resting 


THE    EYE    AND   THE    PHYSIOLOGY   OK   VISION.  591 

during  the  night  and  becomes  sensitive  when  the  shadow  is 
suddenly  projected  against  it. 

From  this  long  chapter  on  the  eye  it  will  be  noted  that 
while  our  knowledge  is  very  satisfactory  in  certain  direc- 
tions there  is  much  that  needs  further  study  and  investiga- 
tion. We  understand  the  eye  fairly  well  as  a  physical  mr 
strument,  but  the  gap  in  our  knowledge  is  in  the  physi- 
ology of  the  retina.  Unfortunately  it  must  be  granted  that 
neither  the  Young-Helmholtz  theory  nor  the  Hering  theory 
explain  satisfactorily  all  the  phenomena.  In  conclusion 
there  may  be  mentioned  some  observations  made  upon  the 
eyes  of  birds  which  may  lead  in  the. future  to  important 
results. 

There  occur  in  the  rods  and  cones  of  the  retina  of  birds 
small,  fatty  globules,  some  of  which  are  red,  others  yellow, 
and  still  others  colorless.  These  globules  are  so  situated 
that  the  light  must  pass  through  them  before  reaching  the 
sensitive  endings  of  the  rods  and  cones  in  question.  One 
can  hardly  resist  the  suggestion  that -these  colored  globules 
of  fat  determine  to  some  extent,  if  not  wholly,  the  sensation 
which  the  rod  in  which  it  is  imbedded  shall  give.  It  is 
evident  that  the  red  globule,  for  instance,  will  absorb  all 
the  other  colors  and  permit  only  the  red  to  pass  through, 
and  so  stimulate  the  end  of  the  rod  or  cone.  Similarly  the 
yellow  globules  will  permit  only  yellow  light  to  pass  through. 
One  feels  tempted  to  believe  that  there  may  be  globules 
answering  to  the  entire  scale  of  simple  colors  and  thus  the 
retina  become  a  veritable  color  sounding-box,  its  physiology 
somewhat  analagous  to  the  basilar  membrane  of  the  ear, 
with  its  strings  attuned  to  the  various  vibrations.  The 
many  individual  rods  and  cones  might  each  be  provided 
with  some  contained  colored  globule  to  permit  only  that 
light  in  question  to  pass  through  it  and  affect  the  retina. 
In  fact,  it  would  be  as  if  each  rod  and  cone  had  a  little 
colored  plate  of  glass  spread  before  it  which  permitted  only 
the  light  of  that  color  to  penetrate  it,  and  consequently  to 
stimulate  it  to  a  sensation.  May  it  not  be  possible  that  in 


592  STUDIES   IN   ADVANCED    PHYSIOLOGY. 

the  human  retina  there  are  such  colors  which  we  are,  how- 
ever, not  able  to  see  because  these  small  globules  might  so 
blend  their  light  as  to  appear  white,  just  as  the  individual 
colors  of  the  spectrum  blend  into  ordinary  white?  This, 
however,  takes  us  into  the  domain  of  guessing,  a  procedure 
which  is  not  always  scientific. 


14  DAY  USE 

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